Bikini Realty
The Bikini Realty is a realty that appears in the episode "Opposite Day," when Squidward wanted to sell his house. Patty Rechid was also shown working for Bikini Realty in "Truth or Square," when she sold SpongeBob a house.
The Bikini Realty is likely responsible for all realty affairs because the company sold two of the main character's houses, most likely more of them.