Owner VOIDED MY CONTRACT!!

What is the name of your state? Texas
Heres the situation. I sold my mobile home to my wife's uncle for $15,000. The terms were $300 per month and a thousand down. $300+ is still owed on downpayment and heres the tricky part. since January of this year, I have been bypassed. I bought the home and it is still being paid off at $250 per month. The mobile home is supposed to be in my wife's and in my name. We signed a contract. Because he is family and in financial trouble i have let the fact that he is paying mrs sharp(whom i bought the home from) $250 per month. So I've been out $50 per month since january, actually prior to that but jan is good. Well come to find out apparently the original owner mrs sharp changed the contract into his name, without my consent, also now she is suing to evict him and to gain full control over the home. She has never notified myself or my wife. He states that he paid october, but she states that he did not. He was going to pay again and she refused payment. well his wife states that she got mrs sharp on tape refusing payment. Again I have never been notified of anything. Don't see how she can evict them when I signed contract. Assumed she would have sued me if it were still in my name. Now if she gains control then I have no legal right to collect the funds owed to me. Do I have a case against her for trying to go around me after i signed a contract and it was notorized by the state?