How can I resolve the conflict between my parents and help my sisters cope with depression?

we r facing very tuff life,conflict beteen my parent due to a women, my mother opnion about my father ,built a relation with other women without nikh,he continue with her contact, my mother try 2 stop that contact but he forbid at front of us,but reality is many time ph call trace, now my mother became cancar patient, my mother live with us but my mother not talk with my father,u can say isolation at home, my father is vary agressive behavier, he is very irresponsible , at minor issue he create a big problem, kindly tell how i resolve that matter, v r 5 sister & hihgly depressive due 2 thart act,