While I actually consider multi-generational housing a good thing, let's ignore that since the reason people aren't moving out is financial and not social.

The question is whether UBI is the best way to solve that problem (and others) and I have yet to see data that can be reasonably said to actually be universal for a region. The closest thing I know of is Alaska, and their oil payments are too small and their economy too remote to say much about larger payments in a larger economy.

To me, because money has a social and psychological value to it, what works on an individual level has no guarantee to transfer to a societal level. I would be very interested to see UBI practiced on an entire economic zone, but good luck getting anyone to volunteer.