How do you deal with an abusive situation and still help someone who is ill and needs your help?

My mother is ill. She has a sarcoma and was going through radiation. Two days ago she was rushed to the hospital and she is now on a ventilator and listed in critical condition. I was told that they thought it was pneumonia. If it wasn't for my dad, I would have been at the house helping her and would currently be at the hospital. My dad is a control freak. When mom first became ill I came home to help. My dad made it impossible to stay with them. He isolated me by not allowing me to leave once I got home. I couldn't go anywhere unless he drove me. He was abusive and put me down. Eventually, I got away. He threatened that if I didn't come back he would accuse me of stealing and have me arrested. I told him I wouldn't come back because of the way I was treated and that I didn't steal anything so I couldn't be arrested. Mom had a close call and my brother and I went out to get mom to the hospital. He took a swing at me and told me that mom's illness was my fault and that he would murder me if he thought he could get away with it. I left and have not been back. Now dad is trying to convince one of my teenage daughters to help him. I am petrified!! He is a loose cannon and I am scared. What should I do? I want to help my mom but since I won't help the way dad wants me to I can't even see my mom at the hospital!! I feel guilty but I am also afraid of what my dad is capable of! I don't know what to do and I am scared