How can my husaband give up his rights to 2 of his daughters that he just found out they were his?

Short answer is he cannot. If he is the biological father, he cannot terminate his own rights. If the mother were to bring an action for Termination of Parental Rights (TPR) against him, the Court can grant that if certain circumstances exist, but he cannot terminate his own rights.  To zoom out a bit, the law gives parents rights, and imposes obligations. The most common example is that a fit parent has the right to parenting time, but an obligation to pay child support. If I have a right, I can waive it. No court can force a parent to spend time with their children. An obligation is different. That parent who does not want any parenting time can still be forced to pay support, and if they have no parenting time, that support will be even higher. So, your husband cannot be forced to see these children. I don't know what that does to kids for a father to say he doesn't want them because of mom's drama, but legally, he does not have to exercise his rights. To the extent he has obligations, child support, payment of medical bills, exchanging yearly income information, etc., he can't lift those from himself.