A. How did you obtain the possession without register the flat in your name is so arcane?
B. Before entering into the flat it should have registered in your name. Have you entered any Sale Agreement towards your flat with the builder? What about the other flat members status?
C. Issue a legal notice to the builder to register the flat in your favor immediately. You can approach the Consumer forum under the deficiency in the Service and Unfair trade practice against the builder in the event of failed to register the flat in your name. And also you can claim the damages under mental agony.
D. Once the all flat members obtain the legal documents with their respected flat through the registered sale deed, then only give green signal to establish the Association.