You have to sell a house to the Jantart Family.
An easy way of getting this is to load up Uninhabited House and immediately sell it.
Another profitable way is this:
Buy the house with uninvited guests.
Make sure to clear out all of the furniture, clean the house, and to put in classic furniture and wooden furniture, as these are what the Jantarts love.
Put a rug in the living room.
Demolish the walls to the home office and move the kitchenette into it.
Make sure to have a few plants along the wall of the hallway.