documentation during asset distribution after death

My grandfather died recently. In his will, it was mentioned that all of his assets are to be equally divided among his two daughters. Elder daughter is my mother and she is also the joint holder of all bank accounts belonging to my grandfather. My mother wants to transfer half of the total amount in my grandfather's bank accounts to her sister. I want to know, what documentation do we need to do when my mother issues the cheque, so that her sister cannot cause any dispute in the future ?