Grandfather gave the Ancestral property to one son other wants share

In 1982 , Only 3.12 acres of Ancestral property was given by my grandfather to my father telling rest will be given when divide among other members, as my grandfather was not keeping well and my father was elder son quit government job and asked to look after all household activity, in which undivided property was more than 25 acres, also there were houses, sites which was not divided between other 2 sons and 4 daughters, but my grand father expired in 1985, property was divided in 1997 between members of family in court, but 3.12 acres land is not mentioned in partition deed, but now in 2015 when we wanted to sell 3.12 acres of land all family members put case asking share telling it's ancestral property, from 1982 till date RTC and all land records are in my father name, is this case valid after so many years after dividing,. ? My father got less share during partition as they considered 3.12 acres during partition,.