Rights of grandchildren over grandfather's property if father died

My grand father has 4 sons and 4 daughters.Two sons including my father and one daughter passed away.At present my two uncle one of whom is not mentally sound and three aunties who are married are there.my father mutually seperated (not through court) when me and my sister were in class one.But after my Grand father,Grand mother and my father's death they divided the property without our knowledge.When asked for our right my uncle said that my Grand father legally declared my father Tajyaputra (removed him from legal right) before my father's marriage which we are not aware of.But I had seen my father staying together along with my grandfather grandmother and us in my childhood.what shold I do