Tonton Streaming The New Addams Family (1998) S1E34 - Close Encounters of the Addams Kind

Aliens looking for a power source trace it to be at the Addams house. After researching TV shows from the seventies to learn Earth culture, they come posed as Greg and Marsha Brady. At the Addams house, they discover that the power source they need is Uncle Fester, and they have a dance contest with Morticia and Gomez to win him. However Greg and Marsha lose, but after explaining their case, Gomez comes up with a solution.