My legal rights

Due to space constraints and other reasons, I left the premises/flat of 1BHK (in Mumbai) which were in my mother's name (on rent receipt) in 1980-81. I shifted to another city. Before this,I was staying in that house with my family and my brother's family and my father and mother. My father passed away in 1984. Till that time both my parents stayed alternately with me and my brother. My mother continued the same practice of staying alternately with me and my brother till her death in 2003. The flat for which she had the rent receipt in her name, she had made a will stating that one of the two rooms in the said flat would remain in my possession and the other in my brother's possession. However, as a family arrangement (undocumented) my brother enjoyed the possession of both the rooms and paid the rent all this years. Now the landlord is planning to go for redevelopment and my late brother's family staying there has given a consent for the redevelopment offer without including me anywhere in it. What is my legal position ?