Property problem

Hi sir, I'm here with a big problem, my dad's grandfather has a huge amount of land in a village still registered on his name, those days because of some diseases they had to leave the village and whole of their property to save themselves, and my dad never knew about the land, unfortunately my dad's grandfather and father is no more in this world and even my dad is very old now he is now in his 80s, so somehow we got to know that there is huge amount of land, we tried to contact the people different landlords to ask about our land, but there are some people who are saying that they will help us but, they are saying that they won't show us our land, they won't exactly tell how much land we have on my dad's grandfather name, and they are saying we will find on our own and we will sell the land on our and we will take 50% and we will distribute 50% among you people... The only thing I want to know what's the legal way to find the total amount of land registered on my father's grandfather name? Pls reply me as soon as possible sir, because if we don't act it would be very late for us and finally those culprits may do anything to acquire our land by wrong means.