What is the ruling on someone who acquired a property from the state with a contract, knowing that the state had seized it from its original owner without right or compensation, and then the acquirer rented it out and benefited from it for years before the property was returned to its original owner? And what are the consequences for each of the acquirer, the tenant, and the original owner?

The state is not permitted to expropriate anyone's property except for a legitimate, recognized interest, along with the obligation to compensate the owner appropriately. If there is no legitimate interest or if compensation is not provided, then this is an act of usurpation (ghasb), and the usurper and whoever possesses the usurped property must return it to its owner. The state has done well by returning the usurped property, and the owner has the right to the rent of his property for the entire period of usurpation. Furthermore, whoever rented the property knowing it was usurped must repent and return what they benefited from to the original owner. Disputes concerning these matters should be referred to the Sharia court for resolution.