Unregistered Will power

My grand father (i.e my moms dad) in that family they have two daughters and a son for him. My grand father put fight with his son and makes suside by put fight with his son and he does not make any will at that time. We suspect that he made a forgery will to acquire all the property. I am residing in Tamilnadu. My question is Are any possibilities to change the property by using unregistered will???? Is unregistered will be accept by court or Indian government??