Do you have a child support order for him, requiring him to pay a certain amount of child support every month? If you don't have that, get that now.
He can relinquish rights to visitation, but he can't relinquish responsibility for financial support.
And I wouldn't tell her he doesn't want to see her. I'd just say he's estranged from his family and leave it at that. Don't single her out as someone he's disowning, even though he is.