Ancestral property divsion

Respected Sir, Myself Ramya.I am third daughter of my parents.We are four sisters.My father got a pysho attack when I was 2 years old.My eldest sister is married.She and her husband were taking care of some constrcutions using the ancestral property.They went greedy .They have registered a building on their name though it was ancestral property.This was possible because the survey number was same for the land which they actually had and the land which belongs to all of us.We also have other ancestral property.When our father went out for walking,they took him to their place.When he was with us,my eldest sister has filed a case for division of property.He was doing okay and could recognise that one of the properties was missing from the document.When my mother other two sisters along with me went to lawyer after my father left the house,he said please don't come with out him.My eldest sister and her husband are powerful and they even acted voilent when we went to them for our property division .We need to get our property divided as soon as possible since all three of us(sisters) have age more than 24 and we need it for our weddings.Can you please what can we do in this case?Suggestions are welcome. Regards, Ramya