Forged our property documents to take bank loan how to defend

One of my fathers friend has taken our property papers Xerox for assisting my father in taking some personal loans, but was not successful, now we have got a letter from court that he has taken a loan from bank making our property as mortgage and my father as guarantee, and the person is not traceable, we are attending the court but unable to do something, instead our property papers are already been mortgaged to another bank since 12 years...he has taken some signatures of my father on some papers at that time asking that its bank forms, my father is central govt employee and half paralysed.