They're snooty people, and the brother is mainly the rude one, so he'll be very blunt with his opinions of things. Elvira isn't a saint either, though she's more crafty with her bluntness. They thrive off of other's uncomfortable-ness (or rather, I do XD) So lash out however you wish, or possibly make nice. I don't think old Morty would mind a bit of member rivalry.