how to stop grand father to sale his own earned property

my grand father is going to sale his own earned property infulance of my uncle who resides within them.grandfather age is around 90 yrs.grand father has 04 son , other 03 are uneducated and don't know how to stop to sale the property, Uncle pressure to my grand father to seal the property and give money to start new business.uncle don't allow to meet any other son to my grand father.kindly suggest is there way to stop them to sale the property