1) Once your grandfather passed away, the property rightfully became your father's asset. 

2)  Because your father passed away after your grandfather, the property passes down to your father's direct legal heirs (i.e., his spouse, you, and your siblings) under the Hindu Succession Act, rather than returning to your grandfather's other children

3)The fact that the mutation or name transfer in government records (Khatauni) is incomplete does not void your ownership. Mutation is simply a fiscal update for tax purposes; ownership is established by the Will and the death certificates of the titleholders

As per Will your father is the beneficiary and the property bequeathed automatically vested on your father upon the death of his father I.e., the testator. 

Now upon your father's death,  his own legal heirs are the successors in interest to succeed to the estates of the deceased beneficiary. 

His brother do not have any rights in the property.