Are the sisters entitled to claim their legal share in the apartment that their father used to rent, and which then devolved to the son after the death of both parents, with him purchasing it with his own money, knowing that the old rental contract extends to those remaining alive from the first generation after the original tenant's death, and does not benefit members of the second generation? And is he obligated to compensate them with monetary amounts as a conciliatory gesture?

Scholars have unanimously agreed on the condition of specifying the duration in ijara (leasing/renting). Therefore, any law that makes ijara perpetual or links it to the death of the first generation after the original tenant's demise is a law that contradicts the Shari'a, due to the prohibited gharar (uncertainty) involved therein.

Thus, it is necessary to annul the contract, and the owner has the choice in the matter. It is not permissible to stipulate that the owner must pay anything in exchange for the annulment. If the owner agrees to sell the apartment to you, this is a separate, valid contract, and your siblings have no claim to it, as they have no ownership in the apartment. Their demand for money is based on their assumption that they have the right to remain in it, but we have clarified that they do not have such a right. A law that contradicts the Shari'a has no effect, and no one is permitted to adhere to it.