Have you tried looking at the Friends and Family forum - there are many in the same position.
My grandmother stayed with my violent, alkie grandfather for many years longer than she should have because of the Christian "I am my brother's keeper".
But Jesus also said "Love each other as you love yourself." Not more than you love yourself. Just saying, you and your mum deserve the same compassion as your father does. Not less.
Also Alanon and Alateen - have you ever tried them. They help so many people.