Is this legal?

[Smilesforever]

Ex hasn’t seen DC since Dec 2015, that was 4 sessions in a contact centre (dv) with the youngest. Ex hasn’t seen the others since Jan 2013.
Court order is for no contact, he can send gifts and the children can choose if they want them. Ex sent somethings at first then we heard nothing for a year, a gift just turned up.
Children want their surname changed.

Legally, can I suggest I no longer claim CSA in exchange for his parental rights? I believe he will be more than willing to accept this offer, but if it gets me into trouble then I think he will do that first.

He isn’t in their lives, is a dv perp and the children feel the weight of his surname. It would also give us more freedom, physically and mentally.

He doesn't have parental rights. He has parental responsibility. He cannot simply give it up. If you were never married you can apply to the courts to have his PR removed. If you were married the only way he can lose his PR is if your child is adopted. The courts are reluctant to take parental responsibility away from a parent but they will do so if it is in the child's best interests.