Bifurcation of Amalgamated flat during redevelopment of Society.

Me and Elder brother brought the Amalgamated residential property admeasuring 820 sq. ft. jointly (ownership 50% each) in 2014. The said residential flat was amalgamated by Society in past (Before Yr. 1990) by merging two adjacent flats admeasuring 410 Sq. ft. each without any change in Building structural plan. The Amalgamated large flat was issued a single Share certificate with 10 share's (5 shared from each 2 flats). Our Amalgamated flat is located on 3rd floor in A wing, whereas in same A wing there exist two separate 410 Sq. Ft flats on ground floor. Further the Amalgamated flat as two separate entry doors and Staircases. Even the Electricity meter are separate. In our registered purchase agreement dated 2014, the Amalgamated flat is shown as Single unit. Further Society consider it as Single flat and not ready to give us NOC despite multiple follow ups. Recently our society has gone up for redevelopment and we approached the to be appointed Builder, He informed the Society Secretary to provide Society NOC and Separate Share Certificate to to divide the redevelopment benefit of 820 Sq. ft flat in two equal small flats. Since society is not ready to support on flat bifurcation, kindly guide us the legal procedure or any suitable process which we can adopt during redevelopment wherein Society NOC would not be mandatory.