I agree that we really never see external family members, except for in apple family reunion. We've never seen rainbow dash's parents, or fluttershy's, we've only seen rarity and sweetie bell's parents once, as well as pinkie pies family, and we all know about applejacks parents, and twilights parents show up for important events because, well she's the "star" of the show. It's more likely that her parents aren't worth showing.