Can I petition paternity for a child receiving survivor benefits from my ex?

Can I petition a childs paternity that is receiving survivor benefits from my ex? His parents, nor his other child’s mom believe this child is his. He was in prison throughout the divorce, she had the baby still married and gave the baby her last name. Final decree was after birth and there is an injunction stating “without child”. Also, court records show he never received final papers and after he was released from prison, he set up payments for both children except this one! Child is not mentioned in the obituary. SSA told me to file fraud paperwork.