Would you do it? DH and I (two kids) and his sister's family (one kid, with maximum of two more planned) are seriously thinking about building a house together across the street from my in-laws. My in-laws have been FIREd for almost 10 years, and currently provide childcare for the three grandkids. Both our households are solidly high-middle income for our area, so we can afford building a pretty good-sized home together, and we both already own our own paid-off homes. They are in their late 20s and we are in our early 30s. Our current rough draft for a floor plan is at 6,000 SF. My in-laws own the lot and will pass it on to us as long as we do a fair buyout of DH's other sibling who lives out-of-state. He has no interest and has said that money is not expected but would be accepted as a nice windfall.
We have been talking about this pretty heavily for the past few months, and know that we will need to draw up a written agreement in case of divorce, or if one family wants to leave, utilities, how to handle disputes, etc. We have spoken seriously about our expectations for cleanliness, use of utilities (heating/cooling), sharing of food, personal space, and there have been no deal breakers so far. The good thing is that we are all open, logical, and forthright about everything, so I don't see any passive aggressiveness, hurt feelings, or slow building of rage happening. We already see each other almost every day, spend vacations together, and help each other out with kids. Being in the same house would just make things so freaking convenient.
Still, in America, it seems like a crazy idea. Wondering what the mustachian take is on this. Bad idea or smart economies of scale?