There is in Flagstaff, AZ, a small state park featuring the home of the Riordan brothers who significantly impacted the development of Flagstaff. We enjoy taking visitors to tour this unique home. Check it out: https://azstateparks.com/riordan-mansion/
The home is actually a large duplex with mirroring layouts connected by a massive common area. The brothers and their families were obviously very close.
When we were looking for a home to share, I often mused that we needed the Riordan Mansion. A duplex would allow us to be close when ED needed help with child care but accommodate our different lifestyles.
Alas, there are no such residences in our area. There are also no “flats” as are found in urban areas: multi-story homes with apartments on each floor.
Now that we are actually living together, I realize those homes would not suit our lifestyle anyway. When ED is away overnight or out late, we need to be in the same residence as the boys. And as we get older, we like our own bed and our own bedtime!
It would be nice if a builder would come up with a suitable plan for multi-families. I would be glad to serve as consultant.