Forgery signature used by my uncles to remove my fathers name from their fathers will

Hi Team, We have a disputed property in Punjab, where my grand father was fighting a case against our neighbors for the last 15-20 years. Before the death of my grand father, he wrote a will under the name of all 3 brothers with an equal share in that property. After the death of my grand father, our rivals offered my father and his 2 brothers an out-of-court settlement/ compromise but my father denied it and decided to carry on with the case against them. Recently we came to know that my uncles have either used the forgery signatures of my father in his absence or somehow got my father to sign a document by misleading him and removing his name from their father's will. This is done for about 2 years while we were waiting for the court hearings in the high court. The hearing date is not declared yet but what should we do? As my father never agreed upon nor signed anything to remove his name from the will, instead he was paying an equal share of the lawyer's fee and was waiting for the outcome. Any productive advice on this would be highly appreciated.