Society Maintenance Charges, OC and FSI

My husbands parents resided in an old rent system building in Mumbai for several decades. In 2005/06 the building went into redevelopment and as a part of the redevelopment agreement they got a slightly higher carpet area( new carpet area of 866 vs old carpet area of apprx 750). However when the builder has constructed the apartment he has constructed it with a possibility to even have a further higher carpet area by breaking walls- In effect a potential carpet area of almost 1250 sq ft. Possession was handed over mid 2010. My inlaws never did any modification work in the apartment and the apartment is in the condition as handed over by the builder. The builder kept promising that OC would come but the building has no OC to date- inspite of 9 yrs since handing over possession. Recently some months ago the builder communicated that BMC has given permission to increase building FSI from 2.5 to 3 and has issued an MOU to each flat owner to cough up apprx 15000 psf for additional FSI which can increase the carpet area from 866 to almost 1250. OC will be obtained post these changes. All the other residents have signed the MOU and the builder has gone ahead with executing the same with BMC. My mother in law has not signed the MOU as she does not need any extra FSI- she does not even live there anymore and the apartment is locked. My questions are: 1) Since my mother in law was an old tenant( she is the only old tenant in the building-all the others are purchasers from the developer or resale flats) does she even have to pay for this extra FSI.. 2) Should she not want the extra FSI and refuse to pay The buider says then BMC will come and do some internal sealing of walls- should BMC do this who is responsible to repair the flat to have it in an original condition- considering my mother in law has not done any modifications in the apartment whatsoever and it is exactly the same condition as was handed over by the builder in 2010. Neither did she ask the builder to construct the apartment in this manner. All the other residents have broken walls and done several modifications utilizing extra FSI as way back as 2010 ! 3) Further when it comes to maintenance charges the redevelopment agreement stated that she will be charged @ 4 Rs psf until the builder hands over to society.. Further there is another clause that says that builder will hand over to society within 8 months of OC. However the society was formed in 2011 ( though no OC) and since then she has been levied maintenance charges of close to 50000 Rs per quarter for the 866 carpet area. There are 14 units in the building- hers being the smallest and i believe they are following a fixed rate for all unis. My question is can be charged this amount for maintenance or should she be charged 4 Rs psf until OC comes? Also how can she get a detailed breakdown of the line wise components of maintenance.. Any questions to sociey iis basically being ignored by the committee members.