Father died when i was minor now sisters son asking share in it

my father died when i am minor in the yr 1962. my mother and sister become guardians. after i become major all the property will come into my name (1982). In 2006 my daughter put case on me for her share (1/3). in the year 2010 my mother died, before she dieng makes death will (2009) in the name her grandson (my sisters son) and now he was claiming her share(1/3). Can anybody help me to solve this case. She was paralysed on 2009.