Property Ownership Transfer from Grand Mother

Hello All, Please guide us on what to do for the property problem below. Currently the property which we own (building) is in the name of my grand mother. She has four children - 2 Male and 2 Female. Out of the 4 children, only 3 are alive. The property which is been described was built by my father (deceased) 30 years back. We want to make it legal with respect to complete ownership of the property. My grand mother is not alive and my father is as well not alive. We have death certificates of my grand mother and my father. There is an affidavit which we have taken from all the other 3 stating that they don't own our property in any form. Please help us get the guidance on the following questions. - What are the best economical options which we can transfer the ownership completely so that we can say that my mother is the sole owner of this - There are bunch of options given to us earlier when discussed with several of the family members - Settlement Deeds, Partition Deeds, property mutation etc. for which we have no clue on what should be the best approach Thanks for reading the query and sparing sometime time to respond.