Is Gift Deed revokable after Will has been made...

My father made a will of our ancestral home, we are two brothers and two sisters, giving us equal portions, in September 2013. Since, only the elder son ( my Brother) lives in the same city, and everyone else visitsed my father in every six months. Elder son was around. He's himself a lawyer. My father in his final days didn't didn't keep well and Doctors gave their answer. In October 2014, father had become senile, Elder son took him and made a gift deed stating that the ancestral home has been gifted to him. He also got the will cancelled. Father expired in Dec 2015... No one knew about the gift deed till then. In March, everyone asked for their share, Elder son replied that Father had gifted him the home, and no one had any claim in it, he kept us in the dark... I just came came to know that we got to object to the gift deed before 3 yrs, that is October October 2017. I wish to know if going through the court, things can work work out or not... I mean I've got another technique, the local MLA is a big time goonda, but he'll take 15-20% of the total value of our shares... But he'll be swift... It's his everyday work. People are saying that the court will take years... What should I do ???