2 Associations within 1 residential apartment complex

No. There can be only one body. It is the builder's responsibility to see that all new owners become members of the association. Their sale deed will have this clause. Please check with the builder. You can file a consumer complaint against builder, the other association, BDA, etc to ensure there is only one association. Please note that this applies only if they also have undivided share in the same property.

Thanks a lot sir. In that case, since phase2 owners are not willing to share/merge their corpus fund and maintenance collection fund with the existing association's funds, should we try convincing them towards a model where there is just one association, but there is 2 separate funds and 2 treasurers one from each phase? With one common president to bind the two groups. Does this model have any legal issues, or is it not wise to do in any perspective? All our attempts to convince to merge both the funds are going waste and is only adding fuel to the lack of mutual trust that exists between the 2 groups. Thanks a lot for your precious time and valuable guidance.