Gifted Property

Hi, My parents when got married 50 years ago, My father's sister in law (the property was on her name) gifted a house in Hyderabad as a marriage gift but no title change or written consent on that regard happened. She died very long back and my father's elder brother continued on her word. He died 20 years ago too. They have 3 children of their own and all knew that this was a gift from their mother to my father. There is no WILL of their parents and therefore no mention of this property as inheritance. around 15 years ago they (middle son and daughter) sent a notice for us to vacate the house claiming its their Mother's. we replied to that notice legally and nothing was pursued from their side The eldest son who respected their mother and parent wishes registered the house on my Mother's Name although we did pay him the value of land around that time and did a proper sale deed. at present in land registry it is on my Mother's name based on that sale deed. Now we would like to construct or sell the house and would like to know what legal position we have on that house and where we stand as per law. your expert advise is highly appreciated. Thanks