My fiancé is divorced and recently found out that two of the children he is paying child support on are not his kids. How would he go about signing away his rights on those two children?

If he isn't their father then he doesn't have rights. However, I think your question is how does he get out of paying support for children that aren't his. And the answer is to consult an attorney.

There is too little info here for us to advise conclusively. Without knowing the age of the kids, whether his name is on the birth certificate, how long he has benn divorced and other info, we can't really say. You need an attorney to advise how to petition Family Court to change the support arrangements.

I agree with ScottGem, consult an attorney try to go with someone who has experience in family law do some research before going to see the attorney. As well bring all the documents to your consultation, us attorneys like to have all the information right away so we can let you know what your chances are and how to go about proceeding. Good luck