This has a high likelihood of disaster.

My sister and her husband moved in with his parents. They have no kids so no issues of spoiling kids, etc. It seemed like a good deal for all parties until the mom and dad really started to go downhill. My sister had not really contemplated what being a true caregiver would entail. Plus, she still works and it became clear the parents needed help during the day. My sister was totally freaked out about random caregivers being in and out of her home while she was at work. Honestly, I think my sister was totally naive. Perhaps not having children made it even harder for her to realize what true caregiving looks like.

You are the woman so be ready to bathe your MIL, clean up both their puke, lift them up off the floor.

I might do it, although I’m more likely to move my MIL in with me when my FIL passes. I would recommend finding one of those college roommates questionaires and considering it as applied to your in laws. Are you comfortable having clear conversations with them about parenting your kids and what boundaries and expectations of babysitting there are? If no, definitely don’t do this. If yes, have those conversations, even if the results aren’t perfect at least the expectations will have been set.

Also as others have said, really consider what your life will be like in the new place. What support system will you have? (Who can you vent to about your DH and his family?) Is the culture somewhere you’re comfortable living and raising your kids?

Never.

All our relationships would crumble.

Can you sell their house and then get a new one with an in-law ADU? I would think everyone would still want some of their own space?

Can you afford to buy their house? Depending on their health situation, would they ever need to cash out of their house to fund nursing home support? If it’s a higher cost of living place, would you risk not being able to afford to stay there once they die or need to sell their house? Does your husband have siblings and how does this fit in with their expectations?

I think multi-generational living is really beautiful, but all parties need to go into this being able to discuss upfront the potential areas that could lead to conflict: childcare, privacy, financial implications, decisions about the house (can you change furniture/ decorating, etc.).

That would be a hard no for me.

We have a similar offer. Because that is a drastic change, I’d suggest you to spend at least a month over the summer if possible before deciding.

It can work, but it all depends on the personalities involved. We have insufficient information on which to advise.

Why would you move in with them? Even if you want to be closer, why on earth wouldn’t you purchase or rent your own home? This sounds very strange OP. I agree with the PP who asked whether this is a shady money grab. If one of my siblings did this, I would be very suspicious.

It works for us. There are minor annoyances, but the love and support far outweigh those.

Does your husband have siblings. Is so, without more detail, this smacks of you guys trying to get into the house in hopes of winding up with the house when his parents are gone.

We don’t know your situation so none of us can give you advice.

My parents and my in laws have health issues. Before the health issues or after, we would never live with any of them. It wouldn’t be healthy for our relationships, our marriage or their relationship with their grandkids. In our families it’s much better to visit and they can spoil the kids and then everyone goes home to their routines. My kids, my parents and my ILs all have their routines and can be difficult in their own ways. And DH and I really need our space.

A long flight away from what?

This would be your new home. Is it a place you want to live? Can you work there?

As PP noted, what is the living situation? Would you have your own space or would you always feel like you're "visiting"?

Are you unemployed or facing significant financial hardships?

I can’t imagine anyone moving their family with their in-laws unless there was something significant going on. Without knowing your circumstances, it’s hard to say if it’s worth it.

I will say that things would have to be really dire for me to consider this.

need more details
Is the house large?
What are the health issues?
How much better is the housing and school situation?
What are you leaving behind?

We have a chance to move in with retiired inlaws. Considering this as one of them is having health issues and we want to spend time with them. Its a long flight away but the housing and school situation would be nice.

We have a good relationship but I wonder if anyone has been in a situation like this? What is it like having inlaws in the same house, especially for the children? I'm afraid of them spoiling the kids and disrupting their routines, as there has been signs of this during the contacts we've had so far. Do the benefits still outweigh the downsides?