I have been nominated by my father for the flat

My father expired on 17th April 16 without making any will. I have 2 younger brothers and 1 sister. We all are married. My 2 brothers got married out of our religion and they have moved out immediately after their respective marriage 20 years back. I was staying with my father along with my family in the flat owned by my father and still I am continuing to reside in the same flat. My father when he was alive have nominated me as a nominee of the flat and the society has the records of the same. The flat which is owned by my father we 3 brothers were residing along with my father and mother since 1987. My mother expired in 1999. The day when we all started staying I was burned to run the family as my father had retired in 1986 from his government services. We all 3 brothers were then working even than I was made to pay for all the mandatory and day to day routine, medical expenses which continued till my fathers death. My brothers have not contributed any funds since beginning towards the house hold expenses.After my 2 brothers moved out they never visited the flat where my father along with me and my family were residing. My sister and 2 brothers have not given any NOC to the society for the transfer of the flat to the nominee of the flat. How do I go about ?????