Writing question

I attempted to google this and got SO CONFUSED.

If there is a romantic couple whose parents are cousins, what familial relationship does the couple have to each other?

ETA: Let me see if I can make this more clear.

Alice Callahan and Beatrice Callahan are cousins. Alice has a daughter, Martha Callahan. Beatrice has a son, Mr. Callahan. (He's a loser and bails on his family before the story begins, he doesn't have a first name. I'll call him Bob for simplicity.)

Bob and Martha get married. What's their familial relationship? (If this is incest, help me figure out some way that both of them have parents with the same surname that isn't incest. In the US, cousin marriage is not considered incest.)