Property

Hi, my great grandpa took a plot on lease for 99 years at chincholi bunder ,malad west , mumbai in 1964. He died and the same was looked after my great grandma, and the name on property tax was transferred on my great grandma...... following that plot have 26 rooms including some shops, out of which 25 rooms have been sold to tenents and they used to give a nominal rent to my greatgrandma........ later due to medical issues she died last year and she made a will in my name and now i have occupied one room from that 26 rooms, and soon after the death of her , the tenents have made welfare society. now please suggest what can be done and what is the process to get our name in that property...