What if my grandma's will says I inherit her entire property, but my dad says it's all his?

If my dadi (grandma) wrote in her will that I inherit everything, but my dad disputes it and says he's the real owner, it'd be a messy legal battle. Under the Indian Succession Act, 1925, and the Hindu Succession Act, 1956, if Dadi's will is valid and the proper procedures were followed, it'd be a tough case for my dad to crack. But, if it comes out that the will was forged or made under coercion, or that Dadi was under undue influence when she made it, the case for my dad would be strong. The courts might also consider the concept of "family arrangements" or "mukti" (gift) under Hindu law, where property is given to a family member without an intention to transfer the ownership. What do you think would be the outcome?