Property dispute with father

Whether registered or not, a Will must be proved as duly and validly executed, as required by the Indian Succession Act. Once a Will is registered, it is placed in the safe custody of the Registrar and therefore cannot be tampered with, destroyed, mutilated or stolen.So your father cannot transfer or sell the property

1. Collect the copy of the Will executed by your grandfather,

2. Apply for probate of the said will,

3. After the will is probated, you will become one of the share holders of your grandfather's property,

4. Your father has no right to deal with the said Willed property.

How did you come to know that your grandfather bequeathed all his property to his three grand children?, have you seen the Will yourself,  do you have a copy of the Will in your possession?  how will you be able to challenge your father's proposal to sell the property in the absence of Will, until you are not confirmed through documentary evidence, you will not be able to lodge a criminal complaint against your father for cheating also. 

Arrange to procure the Will, apply for grant of probate  of the Will and accordingly try for inheritance of your legitimate share, for all these you take the assistance of a local lawyer and proceed as per his further advise.