What are the procedures and rights to become a deem member

I am from Mumbai, In my case we are two brothers and one sister, The apartment was purchased by my father in 1978, he passed away leaving behind wife and three kids as a legal heirs. Later mother also passed away in 2014. In 2011, one of the siblings applied for deem membership with the Society without informing the mother and two siblings, The Society has not replied till now. He and his family are living in the flat since 1987 till date , the other two siblings are staying abroad but holding Indian passport. They visited their mother regularly. The other two siblings came to India and filed a case with Deputy Registrar which resulted in deputy registrar issuing an order to the society to admit all three legal heirs as a members of the society. The elder sibling appealed against the order with Deputy Registrar claiming that he is a Deemed Member, as the Society has not replied back to his Application according to the law, My Question is, is he a Deemed Member. Pls clarify the above and what rights we two have in the property.