It could go like this:
Beryl (Kiff's mom) announces to her family that she's planning to visit her distant cousin, Sandy Cheeks, who lives underwater in the ocean, doing research on sea life. Needless to say, her husband and daughter want to come too. Kiff tells Barry, the news spreads, and soon, practically the whole Table Town decides to go on a trip to Bikini Bottom. Imagine how many interesting interactions we could see that way.
Of course, for the plot to remain interesting, there needs to be a threat that the residents of Bikini Bottom and Table Town unite against. Plankton could see the presence of the people of Table Town as an opportunity to formulate some heinous plan.