Custody rights if not biological parent
My stepdaughter had a baby (now 2 years old) with two men being the possible father. The one she was with when she found out took full responsibility knowing this. He signed the birth certificate and another form stating he is the father and would never dispute that and they got married. They have split recently and she is with the other possible father and wants to get a DNA test hoping the one she is with now is the father and wants to take all rights away from the one who signed the birth certificate. My question is does the father who signed the birth certificate have custody rights if it is proven he is not the biological father?