The high court judgment will not apply in your case. It is illegal for the builder to negotiate with individual members. It is illegal also for the Chairman, Secretary or any other Managing Committee member to choose a particular builder and tell him to negotiate with individual members. It is quite possible the Builder would have either bribed the Managing Committee members or given them a better deal in comparison to other members. The members may or may not be will to sell their flats. Many of them may be thinking they have no alternative but to sell to the builder. You have three alternatives available to you1. Make a criminal complaint to the deputy registrar having jurisdiction over your Society. It would still be better if you meet and discuss with the Registrar before submitting a written complaint.
2. File a complaint with the consumer court. You will have to check whether the consumer court will accept your complaint under the Consumer Protection Act, 1986. The Consumer Court may not have certain powers of a Civil Court, as given below. In your complaint the Managing Committee, all the members who have agreed to sell their flats and the builder should be opposite parties.
3. File a complaint before Civil Court impleading all those mentioned above as the Opposite Parties. There must be an interim injunction against all the opposite parties mentioned under 2 above. Your complaint should state among other things that there is no transparency in the whole affair and the builder may be giving different terms to different terms members depending on their resourcefulness and influence to turn the tide in favour of the Builder. It is also likely that either the Builder or some members may be having political pull. It is also likely that the builder may already have got a coveat against any interim injunction as suggested by me.
You had said that 20 out of 24 members had agreed. Have more members agreed now. You have to educate the members that they are being tried to fall into a trap. The terms for one member may not be the same as another. The builder is trying to byepass collective bargaining and thinks that if only a few are left, they can be evicted. This is cheating and high-handed action.