Find the properties in mumbai with property owner's name

I want to know all the properties in the territory of Mumbai, Navi Mumbai and Thane, registered under the name of my grand father. How to get the details about all his land holdings in the above mentioned area.

Where should I go. Whom should I ask

Though not so easy task.......... but fix some date of ownership record and file RTI with head of townplanning officers, where records of property cards is maintained. ( https://www.e-stampdutyreadyreckoner.com/Property-Card_-Offices-MSD.H T M L), for the property held by your GF on such and such date; Hope, thereby some way may come out.