I want to get my parents divorced

I'm second girl child to my mother(I'm currently doing my internship in MBBS). She is working as a government teacher and my father is a police. Even though she is working he had never given financial independence to her. Her card always stay with him.They're married for 26 years. (My sister is happily married for 4 years, living with her husband and baby.) He made my mother suffer a lot since they got married. He used to hit her abuse her torture her both physically and mentally. He got 5 sisters they are also used to torture her. Being a very loyal loving caring woman,she somehow managed to live with him, because of her love for him and burden of having two daughters. I have never seen him truly appreciating or loving my mother since I born. Do you think he can't appreciate woman? No He used to talk to women in a flirting way since marraige, he used to have two to three potential contacts. In the recent days he is maintaining one Facebook account and using it to talk to woman, manipulating them showing he's a good person. He is talking to two to three woman on phone daily. Recently my mother fighted with him in regard of this and yelled to the woman who is talking to him on phone. But he never changes.. Even today he didn't stopped talking to her. I don't want my mother to live with him anymore. I want them to get seperated as soon as possible. He won't agree for divorce. What should I do now?