you seem to have a lot of miscommunication and misinformation
first of all beyond the agreement to sell the builder is not required to execute any separate sale deed with the unit purchasers
it appears from your query that the builder has submitted the property to the Maharashtra Apartment Ownership Act and executed a Deed of Declaration to form an Apartment Owners Association
thus the builder has to register separate Deed of Apartment with each unit purchaser
as regards the conveyance of the land and building on it, just check the Deed of Declaration as to what is provided in it, assuming you have its copy. Else you can obtain it from the sub-registrar's officer by applying for a certified copy
it appears that the builder has not formed a society under the Maharashtra Societies Act and has instead formed a condominium under the Apartment Ownership act. So share certificate is not required since that is issued only when a society is formed
i dont understand how the individual names of unit purchasers can be included in the 7/12. It is the condominium's name that has to be entered in the 7/12 and with it the names of the apartment owners
7/12 is anyway not a title document as it is only for revenue purposes
your title document is your registered agreement to sell
the unit purchasers cannot intervene in the pending arbitration case since that is a dispute between the partners of the builder firm with which the unit purchasers should not be concerned
as regards discrepancy in carpet area, a rectification deed can be registered
but if your carpet area is greater than what was promised to you then you will have to pay additional stamp duty on that extra carpet area
if the project is not registered with RERA then that tribunal will not have the jurisdiction to try any disputes between the flat buyer and builder
the 5 people will have to file a suit for specific performance of contract ie to enforce the obligation of the builder to obtain OC