Do the Addamses intermarry?

Gomez and Morticia match perfectly and seem to have the same backgrounds. Since the Addams family is so peculiar and different, I can't imagine anyone in it welcoming a typical outsider on the intimate level, or an everyday person wanting much to do with the group. Morticia talks about her husband's ancestors as though they are also hers. Are she and Gomez distant cousins? It might be a traditional practice for the Addamses to ensure that all of the relatives are alike.