Another vote for sending DH with DC#1.

My kids are 2 and 4, and just this past weekend we traveled 3 hours away. They are great in the car now, but the hotel only had one room ready for us instead of 2, and #2 wouldn't nap while we were in the room. Which meant, DH or I couldn't relax and get the 4yo to sit still for a while and rest too. Which also meant, a total meltdown at 6pm because the 2yo was ready for bed (thank GOD the other room was ready by then).

The PPs who say suck it up must have older and/or easier kids. I thing you should be honest with your MIL, that the trip will be extremely stressful for you if you all go because your #2 is so young. You're so sorry to miss it but you and DH have jointly decided that it is best for the family for DH to go with #1. (I mean, #2 won't even remember the trip!) MAKE SURE your DH is on board with this approach. It's up to you whether you want him to deliver the news; personally I have found it better to do it myself because my DH always truncates way too much 'DW doesn't want to go'.

And nothing is worse than being surrounded by family and having someone say 'ok I'll watch the 3yo while you pee' and then 2 minutes later when you return from the bathroom the 3yo is leaning off the boat dock and the relative is engaged in a lively conversation, completely clueless. Been there, it's not fun. Your MIL probably assumes that there will be lots of helping hands but you and I know this is never, ever the case. Be gracious and apologetic and it will be fine. Honestly I think sometimes the 'emotional blackmail' is all in our heads (or so I'd like to think...). Personally I have stopped attending holiday dinners at MIL's friends' home because they refuse, when their own daughter and us both have 2 kids less than 5, to move dinnertime earlier than a 7:30pm start. I stop by with #2 and leave at 6:30; DH stays with #1 until 9 or so. It's fine aside from the line of questioning from MIL's friend (since MIL won't tell her what's up). But MIL does understand because she knows my kids. I think you'll be ok on this one.

OP, what do you mean you don't know how to move them once they are asleep? Easy. Put the 3 year old to sleep in another room. When you are ready for bed, carry the 3 year old to your room with you. S/he probably won't even wake up.

I like the tent idea too!

Also, it sounds like you didn't want to go in the first place. I wouldn't think of a lake an "unsafe place" for little kids, I consider it to be a fun place for them to splash around while I supervised them. Kids that age have to be constantly watched anyway, whether or not there's water around, so I don't think it would make a difference.
Presumably your 3 year old is going to sleep earlier than 8 or 9 year olds, or adults, so even if he talks to himself for an hour, won't he basically be falling asleep in a room and having others join him later? So he won't necessarily have to fall asleep in a room with other kids.

25 miles is not that far. If the sleeping arrangements are really unworkable, explain that the children have to have 2 rooms and get adjoining rooms at the hotel. At worst, you're maybe an hour (but probably less) away from nice, quiet accomodations. Just don't get the rooms without talking to your mil first (or having your dh talk to her) and explaining the situation and how you're looking for a solution that will allow all of you to come. She sounds like a reasonable woman and if there is an acceptable compromise to be made, she would probably welcome an opportunity to suggest it.

I agree with the ones who said that you just need to suck it up and go. Three days is not that long for you or your kids and it will go a long way to keep the piece with your family. And who knows, maybe your kids will do just fine and have a great time. I think you are stressing too much.

OP here - thanks for all the advice and keep it coming. A bit more info:

10:16 - the baby will be 11 mos at the time of the trip. Yes, I am sleep deprived, and definitely hoping some of the sleep issues will resolve in the next month or two. He had severe reflux and is just weaning from meds so we've been reluctant to sleep train. If they do get better I would definitely go, but with the flights and such I dont think we can wait too long to figure this out (and be wishy washy with MIL). Also, I think the baby will wake up with DS1's singing routine - not sure how to move one once they are asleep. I dont think DS1 would sleep in a room with other kids - maybe with grandparents, but SIL usually gets to stick her youngest with them, so that would create the same problem.

10:20 - northern Minnesota.

10:21 - we do travel, but we go places where we get a condo or hotel suite for a week and settle them into their routine as quickly as possible. For ex., we are going to Sea Colony (Bethany) in June (and BTW, invited MIL and she is coming); we went to Mexico with the inlaws when I was pregnant with #2 (again, a condo). We avoid long weekends away like the plague.

10:24 - yes, I didn't realize we would all be in one room. They have rented a second property to fit everyone, so I just assumed we'd be able to spread out a bit. I have also heard several times about how the last time she did this (2 yrs ago) one cousin's wife asked to be moved from the cabin with the septic toilet, and MIL clearly thought that was outrageous, so I am wary of sounding like a princess. But then again, the other families of 4 in one room have kids that are more like 8 and 10, which is a different animal.

I don't know how bad your 3 year old's sensory issues are, but is there any chance he might enjoy "camping" in a tent outside with one parent? If not, just ask MIL to shuffle the guests so that your kids can have different rooms. If it is really important to her to have you there, I'm sure she'll do this. Or just get the hotel room - 25 miles isn't that far, for a special family event.

But did you think that you would actually have two rooms for your family when you agreed to go? I guess I'm a bit surprised by that. You say yourself you don't think you can demand two rooms, so what has changed since you first agreed to go?

I think I would suck it up and go. Your MIL's birthday and a family reunion only comes once. I'm sure it will mean a lot to her if you were all there.

Send DH with eldest DC. They can share a room.

Ok OP, so you will NEVER go on any type of a vacation b/c it interrupts the routine???? I'm asking this b/c I used to be just like you. The entire family thrived on a routine and it was MUCH EASIER for me to handle. BUT, that meant NEVER going away. NEVER doing anything different etc... At some point you have to just jump in and do it. I have 1 DS with MASSIVE sensory issues and 1 DD who hated the car (we had to stop every hour) and she throws up on airplanes. It's not fun. However, we have sucked it up several times to be with family. We are very very careful about DS. We are very forgiving and bend to give him what he needs (so some of our regular rules go out the window). DD takes dramamine on planes and we do a ton of movies and stops in the car. It's a pain, but it has to be this way if we want to go away ever. When we do go away we all sleep in one room. The first night it's difficult, but after that things tend to settle. We all end up going to bed together (I let the kids stay up a little longer b/c honestly it's easier to put them to bed away from home when they are good and tired). I would say you eventually have to give in and try and this time with the entire family may be a good place to start.

I think you should go, but ask your MIL if she can help you with some flexibility. As a PP noted, you can put one of your children to bed elsewhere, then move them together later in the night when you go to bed. Bring a sound machine, and hopefully the baby waking won't disturb the toddler too much. Hopefully they will be able to get some good naps in. That sounds like a REALLY long trip. Just curious, where is it?

I hate to say it, but I don't see how this is a deal breaker. You were all ready to suck up quite a bit. Sharing a room with your kids shouldn't be that much more that you can't bear it.

Sounds like you are sleep deprived a bit? 2 times a night at 11 months, with a flu time job, is rough. This trip is at least 2 months away - can you reasonably expect some of the sleep issues with the younger one to resolve? At least a bit?

What time do they go to sleep? Perhaps you can get baby down before older child goes in for the singing/playing routine? Can you put one child in someone else's room until the other is asleep?

Honestly, I just don't see how you can miss this. I think it would crush your MIL and make you look very rigidly inflexible.

I have a kid with sensory issues so I totally get that aspect. No way I would go.

I don't think you should feel bad about it. Just don't be waffling with her about it. Tell her that you so wish it would work out but that you aren't able to make it. I am sure you'll have more chances in the future once your kiddos are older and easier to travel with.

This is really tough. Is there no way to move around who is sleeping where so that your kids can have a separate room? Or could your oldest sleep with the other grandkids?

I think you have a few options. 1. Suck it up, and plan to take 1-2 days of vacation time when you get back so you can rest from the trip.

2. Give MIL a choice: Tell her that you won't all be able to share a room, and would she prefer a) to move guests around so you can have 2 rooms, b) let DH and DC1 go alone, or c) have you visit a different weekend instead to celebrate her birthday.

I got lucky - I have a great MIL. If it weren't for my marriage we would never be friends, because we have zero in common (different religions, she's rural/suburban/midwestern while I'm east coast city girl, she was a well-off SAHM who plays tennis and bridge, etc., while I paid my way through grad school and work FT at a demanding job, etc) but as a MIL she generally gets everything right. She visits often and helps a lot with the kids including when DH travels, lets me run my house the way I want to, compliments me on how I am raising the kids, etc. I really appreciate her.

The one place she gets a little out of line is that she constantly wants us to travel to or with them. She has never worked and FIL works 3 weeks/month now, so they are always going somewhere, especially a huge lake property they have, and are always asking us to come and using emotional blackmail when we dont. SIL lives near her, has 3 kids and works part time, and takes full advantage of the lake house (and free babysitting), so MIL esp. wants the cousins to play together. For us, however, getting there is a 3 hour flight with 2 kids (3YO and 11 MO) followed by renting a car (so carrying 2 car seats) and driving almost 4 hours. My kids dont like the car (wont sleep in it) and are generally not great travelers - they thrive on routine and dont sleep well in strange places. And we both have very limited vacation time, so if we went as much as she'd like we'd have no time for our own family, and going for a long weekend would leave us totally zonkered given the hellacious trip to get there. And finally, the house is surrounded by water and not child-friendly for young kids (kids that can swim, canoe, and waterski love it), so it's not super appealing to me in the first place. So we usually just politely decline and ignore the blackmail.

Here's the problem. This summer is a big birthday for her. She's hosting a family reunion at the lake, so all of DH's cousins and their kids (all of whom are older) will be there. The place will be packed to the gills. DS1 has some sensory issues and does poorly in crowds. In any event, I was planning to suck it up and go for 3 days because truly she deserves it and she's made very clear how much she wants us there. I know it will be rough - the travel, keeping a constant eye on the 2 kids at an unsafe place, the sleeping in strange places, the crowd - but I was prepared. Then I learned that we will all be expected to say in one room. I think this has to be a dealbreaker. The kids go to bed at the same time, but DS1 talks and sings himself to sleep for an hour, and DS2 is up 2x night to nurse and usually cries/fusses for 45 mins during one of those, and all of this is at home in their usual surroundings, so I expect it to be worse there. I'm willing to not sleep for 3 nights to keep the baby happy, but I dont see how I can put my kids through that.

I looked at hotels - nearest is 25 miles away. I looked at renting a houseboat, for $3000, but I dont think it's safe to have a 3YO who gets out of bed sleep on one. And given how crowded the place will be already, I dont see how we can demand 2 rooms at the house.

Am I acting like spoiled brat if I send DH either by himself or with DS1, and stay home with the baby, or is this really too much to ask? I trust DCUM to tell me straight. Any other suggestions welcome!