Succession Certificate

I have a flat in Mumbai wherein my father died recently and he did not put my name in nomination in Society's records. Now society is asking me to get succession certificate.Also he made a legal will where he nominated only my sister for flat ownership. My sister also died recently and now the flat nomination is still in my father's name.Nomination execution was not done by my sister. In the will it is no where mentioned that who will be the owner of the said flat after my sister's death. My sister also did not nominate anyone.In the will it is mentioned at the beginning that I am the legal heir for this flat alongwith my sister. I have paid maintenence taxes for this flat for past 1 year now. I want to know below: 1. What will be the charges for appealing succession certificate in high court including Lawyer and court fees. 2. How much time would it take to obtain the certificate after filing petition. 3. What are the documents required to be produced in order to file a petition in court. I have my name in ration card/aadhar card for said flat. Also I have some old papers of the plot where this building was constructed. My father never shown me agreement papers also and I was unable to find them too. Please advise. Bhushan Jaykar.