Society's insistence for noc

Sir, I have 2 flats in the Co-operative Housing society where I am residing continuously for last several years. The Ownership Agreement registered with the Stamp Office for both these flats is in the name of my father as the First Owner & myself as the Second Owner. There is no one else in the Registered Ownership agreement other than two of us. Now my father has expired & I am the sole living owner of these 2 flats. Now the Father has expired & before his death we had understanding on this issue with my brother who was given some other property as both these flats were in my name as a second owner & were to be owned by me. There was NO NOMINATION registered with the society in the name of anyone else. Now I have requested the society to delete the name of my father from member’s register based on the Death Certificate submitted by me. But the Society is insisting NOC from my brother to delete my father’s name & keep me as Sole Owner of these two flats. My brother & myself are not in good terms & he may harass me for this NOC…..Please clarify whether society can force me for NOC when I am the Sole living owner of the flat as per registered agreement with the Stamp Office & no one was registered as a Nominee. There is no Will prepared by my father.