What should I do about Sexual Harassment and Verbal Abuse?

First off, I am 14 years old living at home with my 51 year old Uncle and mother. For more than half the school year I just gotten out of I've been riding to school with my Uncle. For that time, he'd masturbate while I was in the vehicle and while we were parked at the store we wait at before my school starts. I didn't know what to do, and still don't know what to do. Then he'd start questioning me and asking if I was okay with it or not. He does carry around a knife and is a Alcoholic so I would always have to say yes. He'd always tell me that's a good answer because if he went to jail then he'd be mad. At home he not only curses and stuff, but throws things around. It's affected me and my mother. Me and my mother don't have a good relationship, so I'm scared to tell her about the Sexual Harassment thing. She has noticed he does act like a pedophile sometimes, and has told me if he ever touches me in any way that she'd kill him. I don't want my mother murdering anyone. I've come down with Manic Depression and Mild Schizophrenia, and I believe it's due to this. I've asked this question before, and people make it seem so easy just to pick up the phone and dial 9-1-1 but I can't even call I confidential hot line when it comes to my Self Mutilation without chickening out. I'm just asking for someone who has gone through the similar thing to tell me how to received help, and how they made their mind do it.