Gift deed

Hello Sir, I am from bhubaneswar(state-odisha). In 1991 my father and his elder brother jointly brought a land of 60decimal(30-30each) in bhubaneswar.His elder brother gave his 30decimel share to my father via a gift deed in which he had signed & clearly mentioned neither he nor his children will ever claim this back in future from my father.This was done infront a registar on a stamp paper signed by both parties.But after my father's death in 2014, his elder brother filed a law suit claiming back his 30decimal share citing he has never done any giftdeed ever nor given to my father.My father has not registered this giftdeed nor any mutation is done.Only municipality tax is being paid since 1991 since our possession.Since itz not registered no revenue tax is paid..On basis of this gift deed my father had done housing loan as well as study loan which is also cleared. I want to know as we havenot registered this land yet means it belongs to our father's brother not Us.Second we r staying since 1991.After 23 long years how can he can claim his share by telling lie that he has not done any giftdeed!!!Please help