Why should people care about looks so much?

Don't worry, it sounds like your brother's girlfriend's family is white trash and if his girlfriend believes them then he can do much better. Humans are vain creatures, who admire beauty and base the beginning of a relationship off of appearance. Just know that not everyone is like that and if your brother's girlfriend can't appreciate all the good qualities your brothers has (physical and otherwise) then he should find someone else. Maybe her family would prefer their daughter date a white (american) person, and they see anyone who is not white like them strange and ugly. Don't take it personally, realize they are just small minded, uneducated people, and tell your brother, if his girlfriend says anything like this again to leave her.