I have a fiancé who has 4 children all togther. 2 of which he pays child suppport for and the other 2 kids belong to us. The 2 he pays for are by different mothers. He sees one of the kids all the time but the other one he has not seen since I believe it was may of last year. He pays for this child and is not allowed to see her, the ex says its because of me she says I will hurt the child but I got 2 kids of my own. She won't let him see the child but the thing now is that the ex is now in a relationship with my fiancés brother. The ex has the child calling his brother daddy and everything. Is it wrong of him to give up parental rightss since he is not allowed to have any contact with the child and not allowed to see her. If my fiancé gives up rights for one child do they have to be terminated for all children.

No, even if he gives up rights, he will still pay, and no that doesn't mean he would give up rights to all just that one. On the other hand, he needs to take her back to court, (I know it is a long haul) and tell the courts what is going on. Did they go to court in the first place to file for custody or is this whole thing between themselves?

The best way to deal with this matter is to take her to court that he may receive visitation rights, because if she lies on you and say that you have harmed the kid in someway, you are asking for trouble both from her and social services as well. He needs to get visitation rights from the courts, this way its legal and she can not stop it. Don't approach this matter any other way, cause it may hurt the both of you in the long run