In Terraria only one NPCs can live per house. This mod removes this restriction.

There is no limit by default. Since v3.0 you can set one in the config

This mod doesn't change the NPC Happiness penalty, so vanilla rules apply: https://terraria.wiki.gg/wiki/NPCs#Factors_affecting_happiness

If you want to change the penalty use this mod: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3039634880
And if you want to change how many NPCs need to be in one place for the penalty to apply use this mod: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2995261274

The require chairs setting and max roommates setting ignore pets.

With the require chairs setting it's currently not possible to move a pet into a house where the number of roomates equals the number of chairs. To workaround this, move the pet into the house first and then move other NPCs.