How to safeguard property in absence of proper documentation

we have a small property which is actually belongs to our grand father. In the old days, they didnt have legal documents and it was allocated land. we do not have any documents pertaining to the property on my grand father. Grand father expired long back in 1970's and grand mother has been the owner ever since. My grand father has 3 daughters(2 are still unmarried,55 and 58 approximate ages). Eldest daughter is married.2 daughters who are not married have registered the property on their name and making claim on the property. We are in possession of the property in a little part since 30 years or so. We have tax bills,electricity bills,water bills of our part on my father's name. How can we self-gaurd our share? please help us.