OP, I think 5 dogs is a lot and you are already being very welcoming but I don't think you are totally crazy. You seem totally relaxed about the idea, it sounds like you have a large house and can corner off an area or 2 for the dogs, so you can try it out this year and see how it goes. It also sounds like you've already made up your mind and are going to do it
I come from a dog family too. We have 4 small (10-40lb) well-behaved dogs in my parent's house at the holidays - mine, my sister's and my parents have 2. But my parents are dog people with a dog friendly so for them it isn't a big deal to have 2 more.
I'll just add a few things:
1) Definitely corner off. You'll probably end up letting 1-2 well behaved dogs out at a time to hang out with the fam. And they will be a good distraction/conversation starter
2) Don't count on the tarps saving your floor. The dogs will play/pull at the corners and I bet they are ruffled up in a corner of the room after a few hours unless you are clever about how you weigh them down (with dumbbells or something?)
3) Don't count on a doggy daycare taking the dogs off your hands at the last minute. I'm in DC proper so I might have a skewed perception but most places are fully booked over the holidays and will only take dogs that have completed pre-stay socialization visits etc.
4) It sounds like you're familiar with these dogs but unfamiliar with what its like to have dogs in your home. Most dogs are really well-behaved but be mentally prepared for messes, chewed up stuff, etc. Make sure your shoes/purses are in your bdrm and the bdrm door is always closed.
5) The PPs about crating are totally correct but a non-crated dog might not respond well to suddenly being crated. A crated dog's owner who fusses over his/her dog would bring the crate.
6) My parents use a cleaning service regularly (so does my sister and I in our own homes!) but if you don't you might want to consider scheduling a one-time cleaning after they leave. It's so worth it to have someone come vacuum the floors and the sofa etc. Fur control.
And if you find that you are totally stressed out then consider this pilot program a disaster and never say yes again! Every dog owner will have a few dog sitting options. Good luck!