Partition

Partition can be made by mere declaration to separate, Partition by Notice, Conversion to Another Faith, under Marriage Act, Partition by Agreement, Partition by Arbitration, Partition by Father, and Partition by Suits.

When a division / partition takes place between brothers after partition they will take equal shares in the property. If there are 3 brothers then each one will take 1/3 rd share in the property.

If the property has been purchased by your father and the same stands in your father's name then it is your father's self acquired property and not ancestral property.Your cousin has no right to claim any share in said property.