All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, is His slave and Messenger.
First of all, we say that such issues that involve disputes among the heirs should be referred to the Sharee‘ah courts because they require judicial settlement rather than a Fatwa. However, we can provide the following guidelines:
If the parts of the land vary in value, it is unfair to divide it equally between the two sons who inherited it on the basis of surface area such that one of them gets the area with the lower value and the other gets the area with the higher value. This is an unjust division, and the injustice in this regard is related to two rights, namely the Right of Allah, The Exalted, who made injustice forbidden for His slaves, and the right of the wronged person who was forcibly given less than his rightful share of the inheritance. The wronged person has the choice either to pardon if he wishes or demand his right. As long as the wronged person has pardoned that past injustice and willingly gave up his right in favor of his brother who took it from him, then his brother’s liability has been cleared from this right, and he will not be punished for it on the Day of Resurrection. However, he is still liable for the Right of Allah, The Exalted, Who may pardon him if He wills or punish him if He wills. The Shaafi‘i scholar Ibn ‘Allaan said in Al-Futoohaat Ar-Rabbaaniyyah ‘ala Al-Athkaar An-Nawaawiyyah: “If the wronged person pardoned the injustice and exonerated the unjust person who wronged him, the liability of the unjust person is cleared from the right of the wronged person, but there remains the Right of Allah (for which he will be held accountable on the Day of Judgment).” [End of quote]
This is the answer to your question, “Will my uncle be punished for this act?” As stated above, this matter is left to be decided by Allah, The Exalted; He may pardon him if He wills or punish him if He wills unless he repents to Allah sincerely. If he repents, Allah, The Exalted, will accept his repentance and forgive his sins by His Mercy and Grace.
As for your stance towards your father, you do not have any other option but to obey him and show dutifulness towards him. You do not have the right to claim what he had given up to his brother because he had given up his own right, not yours. However, this does not apply if your father relinquished his right during a fatal illness that was likely to end in his death. This is because the relinquishment of rights, in essence, is a gift, and a gift that is offered during a fatal illness that is likely to end in the death of the gift-giver is executed within one-third of his estate only. What is beyond the third must be approved by his heirs first. So if he gave up his right (to his brother) during a fatal illness that was likely to end in death, and this relinquished right was more than one-third of your father’s estate, you have the right to claim what exceeds one-third of the estate.
Allah Knows best.