Is it permissible to execute the father's will to favor the eldest son with an additional plot of land in the inheritance, and is it permissible to conceal this will?

A will made in favor of an heir is not obligatory to act upon, and the heirs have the right to reject it; based on the Prophet's (peace be upon him) saying: "Indeed, Allah has given every rightful person his due right, so there is no will for an heir." However, it is a valid will, contingent upon the heirs' consent.