What is the Shariah ruling on a person selling land that was entrusted to him as an amanah (trust), and how should the heirs – especially the son who knows of his father's betrayal of the trust – act to restore the rights to their owners?

It is advisable to treat others kindly and avoid animosity. Matters of disputes require judicial intervention to hear arguments and establish rights with evidence, as the Prophet (peace be upon him) said: "Were people to be given according to their claims, men would claim the lives and wealth of others. But the burden of proof is on the claimant, and the oath is on the one who denies." If your brother admits to his father's betrayal, he must return the rights to their owners. If he is unaware, the claim must be proven with evidence. One must be cautious about accusing people of betrayal without evidence, as Allah Almighty says: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin."