Is the apartment my father gave me permissible or forbidden, given that my father reclaimed the land from the buyer but did not return the apartments he took from him, and I cannot know the details of their agreement?

It is better for the questioner to refrain from accepting the apartment as long as he does not know its true condition and that his father and the man are not upright; for the righteous do not accept gifts from an oppressor or from someone whose money is questionable. Nevertheless, it is not ruled as forbidden for him, as the matter is ambiguous, and the usurpation is not certain. This includes dealing with someone whose money is questionable or mixed with usury; in such cases, choosing to leave it is preferable, but it is not forbidden unless it is certain to be unlawful. If a Muslim knows that money is usurped or taken unjustly, he should avoid it. However, if its condition is unknown, the unknown is like the non-existent, and the default assumption for what is in a Muslim's possession is that it belongs to him. But if the man is known to have unlawful money, dealing with him should be avoided out of piety, and if most of his money is unlawful, there is a dispute regarding it.