Release deed made for property against brother without his consent

My grandfather was given a grant by Karnataka Govt in 1983 of 5 cents in Udupi, Karnataka. The RTC in 2013 showed the property being transferred to all the three children automatically. My dad and his sister have signed a release deed in Oct 2013 in favor of their brother. I recently found this and when I confronted my dad he says he was drunk and he was under the pressure to make this transaction. Saying that the transaction was dividing the property into 3 equal share, they got the signature done. Can i re claim this ignoring the release deed as it is ancestral. I am married.