Property issue

My grandfather(mothers father) had a flat in his name. He passed away in 1991. He n my grandmother had 4 children, (1 brother + 3 sisters) He wanted to give the flat to my mother but back then she refused and hence my grandfather wrote that My uncle's two sons would get the said flat. However, my grandfather rewrote the will many times and maybe we donot have the final copy. (Unsure). My grandmother passed away in 2002. Now, my uncle is asking my mother to sign a Power of attorney which clearly states that she is releasing all her rights in favour of her nephews over the said flat and that appointing my uncle to execute all the necessary formalities. My question is, if we were to go by the will my uncle is showing us, my mother is no where related to the flat. Then why is he asking to sign a power of attorney? It also mentions that she is releasing her rights over the flat, wherein the flat was never on her not mentioned in will. Is there a possibility that my grandfather would have mentioned her name in nomination of the property? And how do we find it?? What could be other scenarios ? The will is just written on a piece of paper, no legal authenticity, also, the execution of will has never taken place in front of everyone. The property is located in pune city.