Yeah, hasn't consistently worked out so hot for me when I do more than around 6-7. Sometimes it's fine, sometimes the characters won't even enter the house, sometimes they won't leave it in the morning, lol. There are occasionally problems even with 6, but it's a lot rarer. Had Sadako refuse to leave the house half the day earlier. I originally used to try to cram in as many as I can, but around 6-7 seems to be the sweet spot for me to have as few problems as possible atm.
If they dont enter the house, make sure their territory (blue circle) are include the house, you want them to enter only 1 house because they wont know if the house are full, it up to us the specified it to them.
as for they wont leave in the morning, are they walking inside the house? some time if 2 house are too close to each other, the "exit" of other house are closer, and the """AI""" will chose the closer exit even if it on the other house and they cant reach it, just dont put the house too close.
also, when puting down the bed, dont put it too close to the edge of the inside, I have problem of npc falling to the void before, so far 10 bed with a bed not close to the edge seem working fine for me.