Where is the property located ?
What are the terms and conditions of the agreement of purchasers with the seller / builder ?
Whether your case shall be for registration of Residents Welfare Association under the provisions of Societies Registration Act, 1860 or your State Cooperative Societies Act ?
Whether the case of registration of a Cooperative Society can be termed as "deficiency of service" or covered under "unfair trade practice" for knocking the door of NCDRC, as stated by you? Answer is simple "NO".
It would be better to consult and engage a local prudent lawyer for proper appreciation of facts /documents, professional guidance and necessary proceedings.