Transfer of jointly owned flat after death of primary member

My father and mother jointly own a property in Chandivali Andheri east I.e. the sale deed contains both the names with my fathers name being primary. My father passed away 3 years back, mother and we 2 sons are legal heirs. Both of us are nominees registered with the society. we now want to transfer the entire rights of the property to the elder son. Mother and me are ready to relinquish our rights. Society is ready to enrol the elder son as the primary member since his name is 1st in the nominee list by us completing certain formalities. How do we complete the transfer to the elder son, is gift deed or release deed sufficient and can the property be sold later by the elder son? Thanks for your help