What is long term possession of land to qualify for ownership

Ours is registered housing society on a plot that is still having builders name in PR card. Registration number was obtailed in 1982 and an attempt was made by builder to give conveyance by filling papers in 1987. It was refused on the ground that builders income tax was not cleared under the then 37(I). The builder had given a lease on part of the plot to the original owner of the plot in 1982. The lease was paying rent till about 2000 to the society. Later the builder now with no partnership registration together with the lease holder made a development agreement between the builder 's newly lodged developing company and the leasee and build a 7 story building on the leased land changing shape and size of the leased portion and by breaking few clauses in the lease. They kept society members busy with development agreement terms and finished development without new lease and development agreement with the society and also by using society's TDR and balance FSI on the plot. Currently builder/developer's family members are in process of buying society member's flats. They have bought almost 50% of the flats and are using as their sister company offices. We do not know if the new building has CC or OC or have a registered society or conveyance is given to them. We are in minority and are not paid our rights on the plot and are told now the land has become their property legally. What is our remedy??? Looking for free legal advise. Please help. bmm301@hotmail.com