My husband is paying child support a for a child that may not be his.

When my husband was first receiving the child support papers before the divorce was final, all papers requested child support papers for one child. After the divorce decree was signed (forged by ex wife) it stated he pay for both children. Child 1 he didn't sign the birth certificate however he did sign his right to establish paternity. Can he still do a paternity testing for a child which is signed these forms. During court, his ex refuses him to do a paternity test for the child 1. Which doesn't make sense because if she has nothing to hide then let him take the test. However child 2 he signed the birth certificate. As well as after child 1 was born he had gotten married to her, under the impression that child 1 was his. He had signed the right to establish form because she had told him it was the only way the child 1 could be added on his medical. This all had happened in 2003-2004, we don't have the money for a lawyer. Is there any way we can fight this on our own? If so what do we need to do and how? We reside in the state of Hawaii.