there is a difference between you being the member of the society by virtue of being nominated by your father, and being the owner of the said flat.
You are as of now, the trustee member of the flat. At the time of selling the flat, you have to settle the claims of the legal heirs from the sale proceeds of the flat. In case the legal heirs do not wish to claim their share, they can either prepare a gift deed or release deed in your favour. Then at the time of selling the flat, you do not need to share the sale proceeds with the other legal heirs.
The society has transferred the membership in your name, so now you are eligible to sell the flat without getting NOC from the society unless you want to sell the flat for commercial purpose.
Otherwise, bye-laws no 38, the NOC from society is not required to sell the flat unless specified.
No need for a succeession certificate, if other legal heirs has given release deed in your favour.