This is a pagdi system rented premises on the name of your maternal grandmother's name. now if you have to change the name on you and your siblings, you have to get NOC from her all other legal heirs including the legal heirs of the deceased.
Without this the landlord will not entertain the name change also.
As a matter of fact you are the third generation child to your maternal grandmother hence you cannot claim the property as a right unless her actual legal heirs relinquish their rights in the property.
The landlord may demand exorbitant amount for name transfer because there is no rule for demanding any fixed amount
You first talk to the landlord and negotiate the deal accordingly.