If you let someone into your house and they quit the game in there, do they get back in next time they enter the world? what about after you sell the house?
They will be kicked out after you log out and end up on the street in front of your house. An invitation to your house only lasts as long as you're logged into the game world or you actually kick them out.
Yes, before the time frame I just specified:
1. You couldn't kick people out of your house.
2. If they logged out in your house, then they'd still be in it when they logged back in.
3. If you logged out, they wouldn't be kicked out.
Now (since at least late June to early July):
1. You can kick them out if you don't want them in there any more.
2. When you log off, they're kicked out, regardless of if they were online or offline when you logged out.