Family partition

My father had two wives. The first wife has two sons and one daughter. The daughter to first wife was died in 1952. Through second wife he had 2 sons and one more daughter (who got married in 1977). Due to some constrains in the relations, he has divided his own acquired properties among the children. All the family properties were divided( based on value assessed by my father in to five parts and given away two parts to his two sons by first wife. The family partition was done through a registered deed in 1968. Then he remained till his death along with his part with his second wife and her two minor sons as a guardian. (The remaining 3 shares of the property were held as combined property). He was died in 1970. He has given first charge sheet to my mother (second wife) for his 1/3 share in the same partition deed towards her maintenance. She was died in 1981. Two sons of first wife were also died. One of the grandson of first wife is now demanding for his share in the undivided part (1/3 share) of grandfather after a period of 21 years. I am one of the sons of second wife. Is he eligible for it? Please let me know whether the property given to my mother for her maintenance will be passed on to her children only or it need to be divided again among the four brothers(includes first wife and second wife children). Please let me know that how 1/3 undivided share of my father or mother can be shared?