It is not known how are you getting any rights or interest in your grandfather's properties.
If at all your father and his siblings who have been allotted with less share want to fight against it, they can do it only during the lifetime of your grandfather.
Besides since this property was acquired by your grandfather as a gift from his close relative, it becomes your grandfather's own and absolute property.
Thus this being your grandfather's self acquired property, he has full rights to dispose the properties in any manner to anyone of his choice.
If someone decides to approach court for challenging the Will, it can be challenged only to the genuine execution of the Will and the contents of the Will cannot be challenged.
Don't expect a favorable opinion which would be unlawful and misguing.
You will fall prey to only cheating people if you expect replies appeasing or making you happy.