Paternity Test Needed

My husband is court ordered to pay child support for two children that are not his biologically. He was legally married to his ex-wife when she gave birth to the twins and with him being in the military at this time he was forced to sign the birth certificates. The children actually know who their biological father is and they spend time and receive money from him as well. They live in Texas and the very little contact we have with them; they always let him (my husband) know that he is not their dad and they don’t have to listen to what he says. We have went to court to try and clear this issue up on several occasions, with no success. He has requested on several occasions to be granted a judgement for a paternity test and has been denied. The twins are know 17 and we cannot continue to let this go on. To my understanding we have to take care of this before they turn 18 next year.What can be done in this situation to clear my husbands name from their birth certificates and file a civil suit against their mother for knowingly having the court/DHS help her file this fraudulent case against my husband?