Role of Nominee's legal heir in transfer of ownership

My father owned a flat in a Cooperative Group Housing Society in Delhi which was later made free hold. He expired in the year 2010. Society traced the records and advised in Y2019 that he had made my elder brother his Nominee in the Society records. Before the Society and my brother could complete the required formalities unfortunately my brother also expired due to Covid-19 in April,2021. My father had written a WILL in the year 2010 and had made me the beneficiary of the WILL in respect of this flat and membership of the Society. The Society authorities are insisting that now the legal heirs of my brother has to step in his shoes to complete the formalities and I do not have any local standi. The WILL is not registered and not probated. But it could be probated now. My father resided in Gwalior, written the WILL at Gwalior and expired at Gwalior. The WILL covers another property at Gwalior of which my elder brother is the beneficiary. There is no family dispute.