My sims won't go inside their house when they come home

I'm not quite sure what would cause it but I would check to see if the door itself is locked to everyone. (unless you already checked that and I misread somewhere. Apologies for that :p )

If it's not, then I say you should save the lot to the library bin, delete the house, and re-place the house lot. That's usually my go-to fix whenever my houses act up. Hopefully you find an answer to this!