Property dispute

My grandfather has some farming land and he has six sons including my father. This farming land is our paitrik sampatti as some of it was bought by my great grandfather and other my great grandfather got from his father. Recently a part, which was bought by my great grandfather was sold and rest was declared to be belonging to my five uncles by a wasiyat. I want to know that how can we stop this injustice to our father and how can we stop our land from getting sold. I also want to stop them from doing any kind of future selling of this land. Thanking you