Is the son entitled to own the plot of land disputed with his siblings, and what is the amount due to the mother for her land—is it its value at the time of relinquishment or its current value?

If the father gave his wife's land to his son in exchange for a debt he owed the son, and the husband promised his wife an unknown compensation, and the wife accepted that, then this transaction is void due to the uncertainty in the compensation, and the land remains the property of the mother.

If the sale was concluded with a known compensation specified, then the sale is valid, and the land belongs to the son, and the heirs must pay the agreed-upon compensation to the mother from the father's estate before its distribution.

In case of dispute, recourse must be sought from the Sharia courts.