Relinquishment deed suspect

Dear Sir, My grand father used to won a house in south delhi by expried in 1980, The property then went to my mum, her brother and mother, Then my mama (My mum's brother expired and the property was mutated in my mothers, her nephew and her mothers name then her mother expired in 2011. Today when my mother asked her nephew of selling the property he kept avoiding the question and has now in presented a relinquishment deed after 4 years of her death. Saying you mother gave up the rights of the property to me and i though she would have told you. The deed was made when the grand mother was alive. The nephew has also changed the name on the bills in the electricity office with my mothers knowledge. All the factors appear as though her nephew knowingly wants to extract all the property an money he can. Apart from that the relinquishment deed does not mention the property in entirety, It mentions the ground floor, 1st floor and 2nd floor roof rights. It does not mention the garage or the 2 single room units above the garage. The deed is registered at the sub registrars office with 2 witness, who we have no clue of who they are, nor was this every brought up before. The deeds appears to be registered in haste. Even though the deeds mentions that its being done without any pressure the facts do not appear to be so. What rights does the daughter have and how can the contents of the relinquishment deed be verified.