Abusive family

I belong to a rigidly dysfunctional family wherein my parents and brother have idealistic value set. They consider each other as ideal, though they are not in eyes of other people. Moreoever, they are stuck by this complex that only an ideal member deserves to be happy in life. So my mom sometimes expects that his elder son, my brother, can only get married and have children because they like him a lot. Whereas, because i am not ideal for them, they don't like me and don't want to accept me to be able to live a normal life. So they create problems in my life in some way. Now that when i am getting married, they want to use my sexual energy, especially my mother, so that she could later channel it to my brother who can than reproduce. Unfortunately, he has not been able to do so 5 years after his marriage. My mom considers herself to be the controller of this lust factor of all the male members in my family, including my brother and father. If someone denies her this, she feels insulted and starts neglecting that person or rejects him as being imperfect. She definitely has deep psychological and sexual issues. Please advice, on how do i get rid of my tendency to try to fit myself in to this destructive behavior. I feel that i have been born with a purpose to serve the needs of my family members and feel guilty, unimportant and dejected if i am not able to do the same.. Please advice.