child support, libel

my father is a police officer and he has been lying to us for the past 18 years. he left me and 3 of my siblings to my mother WITHOUT ANY SUPPORT. it was only then that we knew that we are not his legal family when his legal wife talked to my mother telling her via facebook that she is going to sue my mother if my mother won't leave my father alone. my mother had no idea that my father was married in the first place. he even married my mother but USED A DIFFERENT MIDDLE NAME in their marriage certificate and in our birth certificate except for my youngest sibling. please help us. i had to stop my schooling to go to work and help my mother. what can we do to oblige our father for support especially financially?