Grandson's rights in property of grandfather

M hindu, My father having some property. The same purchased by his elder brother from sale of my grandfather's gold n jewelry. Now the elder brother transferred the share of property to my father's name. now he has donated some property to a cunning person and we scared that the guy will transfer all property to his name coz my father is doing blind faith on that guy. My father has kept all original papers to that guy and spend all the time with him. He is neither giving any money at home nor taking any responsibility of home. Can you please advise what we can do? I am the daughter, having one brother and my mom.