Gpa : bda : confirmation deed

Hi, My dad was given GPA in 1989 for a property in bangalore. The GPA was given by a person who got the property through BDA allotment. My dad executed a sale deed in favour of my mother in 2011 and unfortunately he expired in 2013. Everything is in the name of the original owner - BESOM,BWSSB,KHATHA. Now, the original owner's son has gone to the court claiming that the property is his. We decided to settle down the matter in mediation centre and we came up with a deal to pay x amt to them. Can you please let me know what all needs to be done once we pay them the amount ? My lawyer says a confirmation deed is enough and that can be taken to the BDA to get all other documents. We will have to transfer Khatha,BESCOM,BWSSB bill - everything. The original owner has 3 sons, but my lawyer since this is a self acquired property only the owner's signature is enough. Also, we want to make sure they dont come back again in the future. Please guide me.. Thanks for your time. Regards Darshan