Firstly the law should be understood that once a proper partition takes place, the nature of ancestral property extinguishes.
Further, you have not stated that this property came out of ancestors. It was your grandfather's property duly partitioned by his sons.
In any event, the share of property got through partition by your father alone can be subjected to further partition among your father and your coparceners.
The property inherited by your father through the testamentary disposition i.e., by a Will of your grandfather is your father's own property which cannot be claimed as ancestral property.
The property acquired by your father through a will shall become his own and absolute property in which neither you nor your brother can claim a share as a right during your father's lifetime.
Since your father is alive now, he can dispose his property in any manner as per his will and wish and to anyone of his choice.
Nobody can force him to partition and allot his share which is illegal.
Further since your narration is more confusing instead of convincing hence without seeing the relevant papers or property related documents, a concrete opinion about anyone's entitlement cannot be ascertained, therefore produce all the documents before a local skilled and knowledgeable lawyer and get his further opinion on all such further issues.