How do you say it is your grandfather's property, is there any sale deed on your grandfather's name?
If there is no such thing then whether your father at least obtained pattadar passbook ?
Is there any pattadar passbook in your grandfather's name?
Whether your father took any initiative to obtain patta or adangal to prove his title?
What is the basis that he got the property mutated on his name, is he having mutated records on his name?
Even now he can apply for pattadar passbook from the revenue department on the basis of the revenue records held in his name.
Alternately he can file a suit for declaration to declare his title to the property on the basis of the mutation records and gram panchayat ownership certificate.
Consult a local advocate and proceed legally.