Is csa still payable if the children are adopted?

my sister is divorced from the father of her children and she has since remarried. her new husband wants to legally adopt the children and have their sirnames changed so that they have his name. will the childrens biological father still be liable to pay csa if this adoption takes place? the biological father has given legal permission for the adoption to take place. i know we can check this with the csa department on monday, but they are closed over the weekend, and we were just wandering if anyone on here knew the answer!