Bosco and Stewey are actual cousins because Bosco's father, Catfish Hunter and Stewey's mother, Headley are brother and sister. All hail from the lovely confines of Willowswamp Farm in Ligonier, Indiana which you can access through a corn field if you're stupid like me and miss the turn.
Stewey and Bosco don't get along well, I'm afraid. Bosco just wants to be loved and Stewey just wants world domination. Together, they are a recipe for spinster disaster, but somebody needed to be the adult and live her life responsibly and it might as well have been me.