That's awful. Maybe you could sit them all down and tell them how you're really struggling with it and they're really not helping you overcome it? Also look into speech therapy. It works wonders and is worth the money. Best of luck OP.
Family. Can't live with them, can't live without them. Until you turn 18, that is. They're supposed to be supportive, but fuck them. Remember that down the line when they eventually ask you for help. There's no excuse for abuse.