1. this case is governed by the Bombay Rent Act, 1947 which is now succeeded by the Maharashtra Rent Act, 1999
2. as per definition of tenant in both these acts, in case of residential premises, the family members living with the tenant at the time of his demise in the tenanted premises, are entitled for transfer of tenancy to their name and only when such family members are absent, can the legal heirs claim tenancy rights
3. so you need to check first who all were living with your grandfather at time of death. These people will be entitled to tenancy rights
4. however it appears that the rent receipt got subsequently transferred to your father and mother. So you also need to check who all were living with them in the room when they passed away. These persons will be entitled to tenancy rights
5. it appears that your aunt was living all throughout in the room and as such she has a right and claim over tenancy of the room.
6. i doubt if other married aunts can claim tenancy rights since they must have already shifted to their matrimonial homes and would not be residing in the premises at the time of the death of your grandfather and parents
7. if you are claiming exclusive tenancy right then you will have to file a declaratory suit in small causes court in which the landlord and legal heirs of the last tenant and the family members living with the last tenant will have to be made party defendants