Is this correct La familia toma en el comedor?

Not entirely. There are two things wrong. "Toma" is singular and informal. It also means "to take in." This sentence, in English, would read: My family takes in the dining room.

To say your family is eating in the dining room you would write: "La familia comen en el comedor."

If you must use the verb toma, the proper use would be toman.