My grandfather is alive and he has self acquired property.

Youcannot forcefull or through court claim your grand fathers property. Your grand father is having right to declare on whom the property should be. so you try to gain pure love and affection from your grand father. so that he may a write a WILL stating all his properties for his lovely ones. 

Agreed with experts.

If grandfather deceases without leaving any WILL, but leaving the property then you may have a share from share of your father.

Thanks Everyone for your answers.
 

My grand father disowned my father from his property without any legal notice(Paper) from court or from legal authority, But he forcefully took my fathers signature on a personal stamp paper in front of his friends.

In this case what should I do

Since the property is your grandfather’s self-acquired property. He is having right to disburse through his own will.

You can send notice/ file a complaint, stating not to misuse of the signed stamp paper, which was taken by force from your father.