In the decision of Central Information Commission in the case titled Surender Pal Singh vs SDM (Kanjhawala), GNCTD bearing no. CIC/SA/A/2014/000462, it has been laid down that transparency of land records is the mandate as per the RTI Act and it is the duty of land authorities to provide information about land records to citizens.
You can file an RTI to obtain information to obtain the documents and procedures followed for the distribution of your grandmother's property in the name of mother and aunt( wife of my father's brother).
Also, you can file RTI in the Sub Registrar Office to obtain information regarding the rules and procedures to mutate the property in your mother's name.