Property was not partition well by family

My grandfather has 3 sons. grandfather was expired when he was in 30 years then 3 sons they had 8 acres that time they had hard worked and bought 8 acres agricultural land totally 16 acres to my family. my big father got registered 8 acres of land on his name while family combined that to he had bighead to family .that time no one asked him. every one separated on 1995 year.my father does not know nothing that why other two people partitioned agricultural land as their wish. so my father part of agricultural land has 4 Acres.other two got my father has 2 acres registered on his name ,1 acre registered on grand father name 1 acre registered on big father name.so here i wanted to register agricultural land from big father to on my father name but my big father is not accepting to sign so what we have to do ? what type of case we have to put on big father ? pls tell me wont we have any rights on land? we have registration papers on his name. can he do register the land on his sons names or sell now ?