Which is the best option for transferring property - will or gift

We have a two-storeyed house in Kolkata. It is in the name of my widowed mother. The property got transferred to her name after the death of my father as per the will executed by him. We are two brothers and one married sister. Now my mother wants to make a deed in order to transfer the property(the said house) in our names after her death. She also wants to make it clear in the deed who will get which portion so that no dispute arises in future after her death. The problem is that the partitioning of the house among three of us may not be equal. The house in its present form is such that it is very difficult to equally partition it among three of us. As I understand she can do it by executing a will or a gift deed. It is also important to mention here that we do not want our mother to relinquish her ownership of the house till she is alive. Under the circumstances, please suggest which one she should opt for - executing a will or gift deed. Is it necessary to partition the property among the legal heirs equally in a will or gift deed?