• Property bought

I bought a room from a person who was the only son of his mother and father with three sisters.
His father and mother both had died earlier so he wanted to sell his room and shift to village. I bought his room with all legal documents and done all the necessary procedure from court with the help of a lawyer.But now after 2.6 years later he and his sisters are saying that his sisters also have quota in that room,and they are threatening me that they will fire a case in court and will take back there room.I have transferred light bill,water bill on my name,also i have ration card of that address with my name.Now its more than 2.6 years that I am living in that room.
I am worried that can they take back my room by filing case on court saying that his sisters also have quota in that room.As in property sale agreement only that person's sign is there not his three sisters.

Please guide me I am really worried.

thanks in advance