Probated will on ancester property

Hi, I need an advice on below dispute related to ancestoral property. My grandfather had 6 acre of farm land out of which 3 acre land was ancestoral and 3 acre land he had earned in his lifetime. Now after his death in 2003, My one cusion has done mutation of whlole land on his name. he claimed that my grand father had made a will and donated all his land to his name. he had already probated the will and it has been directed by distric court. However in his probate his elder brother and his brother in law has given as witness. Can you please suggest that - 1. is it possible to make a will for ancestor land as well given their son were alive? Can i challenge the probated will on this argument? 2. In the probate, Can i challenge the will on the basis of fraud as his elder brother and his bro-in law are witness? Cant it prove a doubtful will for court? 3. Please suggest how I should proceed so that all land mutation can be rollback to grandfather and then distrubuted to uncles fairly?