Mutation of property

A (husband) and B (wife) became members of DDA in 1979. A died in 1980. The couple had two children C (daughter) born in 1958 and D (son) born in 1961. Both B and D took possession of the property in the year 1987. But before 1987, all payments with respect to the property from 1980 till 1987 were made in the name of B through his own account. In 1986, both B and her daughter C , relinquished all her shares, rights titles etc vested in the property after the demise of A who could have been an original allotee but died before taking the possession long back in 1980. But then even after relinquishing her share in the property , the authority gave joint names on the possession certificate (jointly) in the names of both B and her son D. B expired in 1994 and D died in 2006. Both the relinquishment deeds were duly registered with the sub-registrar in 1986. One of the lawyers has told C, the daughter has also relinquished her share in the property in 1986 and now cannot get her share either throught the court or by any other means. The file in the authority has happened to be misplaced (as claimed by the department). Now I have both the relinquishment deeds with me along with the death certificates , how can I transfer the property in the name of legal heirs of D (Son's family). Also, the NOC of C which has already been taken in 1986 may not be needed now as the lawyer has told us the Relinquishment deed is given only one ? How can the auhtority transfer the property in joint names of mother and son were given in the possession letter when she has already given her relinquishment deed in favour of her son way back in 1986 ? Is there any person who can get the property mutation/freehold, what formalities would be required? I also eblieve Relinquishment deed would not be required again ? Please explain and help me for getting the property transfered in the name of the legal heirs of D.