Transfer of share Certificate and apply for duplicate one

Hello Everyone I would like to know your expert advice. I co owned (50/50) a small flat in mumbai with my father. He appointed me the nominee after his death. He passed away 2yrs ago. Since I don't have the physical share Certificate I asked the society for duplicate one. They said I have to file a fir and submit an application to the society. After which they will conduct a meeting and see what the resultant is. It's been more than a year they haven't taken any action. They are asking for a release deed from legal heirs which is me and my brother as our mother too is no more. My father already made a gift deed of other house without my knowledge and gave his house to my brother. I had my mother's share in the same. That's a different story altogether. Can the society stop me from giving the place on rent? I am not selling the place. From my understanding release deed from my brother is required only when selling the place. Please correct me if I am wrong. Already someone has intruded the property without my knowledge hence being the legal caretaker and 75% owner of the property isn't it my responsibility to look after the place? Can anyone intrude the property without my knowledge? Awaiting your expert advice. Thank you.