Senior citizens harrasment

As it is his self-acquired property, no one can force to give property.  complain against your sister in Senior Citizen's cell.

Since it is his own and absolute property, your grandfather can very well deny and refuse to give her anymore share in the property.

She cannot pressurise him to allot  any share in his property at least not during his lifetime.

He can file a permanent injunction suit against her restraining her from interfering in his possession and enjoyment of his property.

He can also lodge a criminal complaint for her harassment and tortures she metes out to them demanding the property, with the local police or with the senior citizens' welfare tribunal.