Need To Know It Is Necessary To Probate A Will Or Not In My Case

My father was working as a assistant teacher in state government school. He passed away on 1st of May 2019. We found a will made by him by the name of my mother i.e. his wife, my sister i.e. his daughter and myself i.e. his son. Also the nominee mentioned in his service book were the three persons which I mentioned in last sentence. My father's dad has passed away and his mother is alive but due to dispute with her and my father he has not mentioned her i.e father's mother as a nominee anywhere. We (me, my sister and my mother) were helping with monetary support and other things to her. But now few peoples from family are asking her to get part of money which will get from my father's gratuity, provident fund, etc. She has send a notice to government department of my father to not give any funds without her i.e. my father's mother approval. So what should be done in this case. We are willing to help her.