Claim by Step Mother on Registered Gift Deed

My father transferred a Flat situated at Vashi through Registered Gift Deed earned by him self. I being only Son the same has been gifted to me. The Gift Deed was registered on 24th June, 2014. My only sister who got married on 7th June, 2014 and settled. On 18th Nov., 2015 i sold above flat to a potential purchaser. After Sale of said flat my step mother has sent a notice to my housing Society requesting therewith not to issue NOC to me and asked for share. My Housing society is not issuing NOC and threatening to me and new owner by all means. I also sent all the registered documents through my Advocate and well received by Secretary Society too. But Society is not issuing NOC and insisting me to settle issue with my Step mother. Society also threatened to new purchaser and tenants placed by new purchaser. My question is 1. Can Step Mother (basically she was in livein relationship as my original mother was not divorced) make such claim on the said flat. 2. Can Housing Society restrict me and deny to issue NOC. 3. Can my married sister claim on the said property. I have clear title of the said flat through Registered Deed.