If my children's father signs off on the children would he still be reliable to pay child support if there is not another guy figure to legally adopt the children

What do you mean signs off? He would be responsible until another takes his place. There is no signing off unless its for adoption.

There is this myth that a parent can just sign a paper and relinquish their rights. But its just a myth. Only a court can terminate parental rights (TPR) and a court will not issue a TPR to allow a parent to get out of paying support.

So, if your children's father thinks he can sign something and stop paying support, he is sadly mistaken.

Have you read this? https://www.askmehelpdesk.com/family-law/signing-over-rights-read-first-116098.html