Do joint development and sharing agreement give right to do property transfer (registration)

Yes, builder is  saying right owner of property has to execute sale deed with builder as confirming party.

Thanks Bhartesh. As a confirming party, builder's signature would be fine or he needs to mention i am confirming.

Mere signature of builder on sale deed is not enough, builder has to varify that he is confirming party to sell with his signatures.

The property you desire to buy would be from the owner's share in the developed property, which is evidenced by the JDA, hence there is no legal infirmity in it. 

The seller will be the landlady, hence it would be appropriate that the owner executes the registered sale deed in favor of the buyer. 

The sale / purchase transaction is valid and legal.

Builder had done a joint development agreement with the lady and and had given some plots to her. My plot is 1 of the plots coming in owner's share (lady's share). Lady is one of the directors of the company and has given her SPA to a person Mr. X to do sale, represent her etc  in any documentation.

As per builder's board rsolution, builder has given right to do agreement and to execute sale deed to the same person Mr. X.

The lady will transfer the proprty to us and builder will be confirming party. Since Mr. X represents both parties- one with SPA and other with board resolution.

Mr X is coming to registrar office and and will sign at both places: seller and confirming party (builder). Is this OK that one person is representing both the parties?