Nomination in a flat

Hi, we are 2 siblings, myself and my married sister. My father made me a nominee in the flat in Mumbai and upon his death the flat and share certificate was transferred in my name. My sister had given an affidavit, as required by the Society, whereby she relinquished her right in the said flat in my favor. Now, what are the formalities, in case :- (a) I want to become the absolute owner (to avoid further claims from our next generation) (b) If I want to sell the flat within the next 6 months. Your advice in this regard would be highly appreciated. Regards,