My mom has cancer and her husband treats her like crap!?

what should she do, she has to rely on him to take her to the hospital and everythin i dont have a car to take her to the hospital only a learners. He calls her names all the time and picks with me and my brothers and sisters, he starts a lot of drama in our family and were getting tired of it but we dk what to do? there married and he has threatened my fiance from coming here at my dads house because my dad n fiance got into a disagrement. He trys to tell my mom that our family and us kids dont care about her. I heard him saying it tonight and i told him off and he caled my mom a ***** and i called him something i think a coward fould mouth as* and he was a mofo and he acted like as if he was going to hit me and my mom got in the way and told him to stop. we dont want to put up with him but it seems we have to because we have no way around what should we do?