Maternal Grand father property Division

My mother's father (Maternal Grand father) had purchased a house from his own funds. Maternal Grand father had two daughters (My Mother and My Aunt), no Son and two wive's (both died). In his registered will, he mentioned that Ground floor belongs to my mother and first and second floor belong to my Aunt. My Maternal Grand father and my mother passed away and survived by my father, me (only son) and two daugters (married). My mother haven't created a will. My Maternal Aunt is still alive and has two sons, one daugher (married) and daughter in law. My aunt occupied the roof when my Maternal Grand father was ill and constructed half third floor. In the registered will, there is no mention of roof/third floor and is a bone of contention. Till date property is still in name of my Maternal Grand father. I have two concern. 1) How to ensure that I get Ground floor and half share in roof right and my aunt to get share of 1st and 2nd floor and half share in roof rights. How a roof and above floor rights are distributed equaly if it is not mentioned in the will. 2)My mother passed away without will, my father and my sisters are in agreement to transfer my deceased mother's right in this entire property solely under my name. 3) My aunt do not want to resolve the issue and will not go for the mutation or legal division of property. Please suggest what should I do, how I get my mother's right in this property transferred solely in my name. Should I gask my father to create a will and transfer his due property rights to me. How to take a legal no objection from my sisters to avoid any future issues? please suggest in detail? Rahul