What is the ruling on a family remaining in a house obtained from the state in 1979, then it became clear that it was owned by another person, and the son, who was the family's agent, verbally forgave the family regarding the house, while the father, the original owner, demanded they vacate it, then the father died after the court ruled in the family's favor?

The sanctity of a Muslim's wealth in Islam is like the sanctity of his blood and honor; nothing from his wealth is permissible without his willing consent. If you know that the state has usurped this house from its owner unlawfully, then it is not permissible for you to take it from the state, because that would involve consuming people's wealth unjustly and aiding the oppressor in his oppression. The statement of the young man who claimed to be a guardian is not considered valid unless he presents legitimate, credible evidence; for "the burden of proof is on the claimant, and the oath is on the one who denies." The indications suggest that you did not acquire lawful ownership of this house; therefore, you must satisfy the heirs of that man or return their house to them, as long as you are certain that the house unequivocally belongs to their father. You have the right to demand from the state the money you paid it as the price of the house.