Tenancy rights after death of tenant

One Room kitchen was taken on pagadi (tenancy) by my grandfather in 1950s in Mumbai and in early 1990's the tenancy was transferred from my grandfather to my mother with his consent and transfer premium payment to the landlord. My mother passed away due to illness on 2016. My father then approached the landlords. But they did not entertain the letter from my father and verbally told him that since the building will go for redevelopment as it is in very bad condition not suitable to stay and once the new building is constructed my father will get the flat allotted in his name. My father due to illness passed away in 2019. We approached the landlord again for the relevant transfer of tenancy in our names and to also accept rent payment from me and my brother the letter w.r.t. Rent payment. The landlord did not respond to my letter and verbal requests. My Sister in Law, wife of my brother does not stay with her husband due to which she stayed with my father along with his children at the time my father died. Now since building is going for redevelopment by the landlord. She has signed an agreement with the landlord declaring that she is the only family member and surviving tenant and has received advance from the landlord to vacate the room in lieu of 15 to 18th months in advance. The agreement has been registered between my sister in law and the landlord. So far she and the landlord have not shared any documents of related to agreement with me or my siblings. I had personally approached the landlord to know about the transaction and agreement between the landlord and my sister in law. Land lord and sister in law both declined to share the documents signed . Landlord also mentioned that there is a will signed by my father w.r.t. the transfer of his rights to sister in law. We seek your opinion on the above matter how get tenancy rights for my brother and sister