Is it permissible to re-divide a house that was previously relinquished and its value estimated for one of the heirs in exchange for a sum of money, based on the request of one of the sisters who claims that what she previously received was a gift?

It is not possible to issue a fatwa regarding this dispute among the heirs without a complete understanding of the issue, which requires hearing the statements of all parties. The heirs’ relinquishment [of their share] to their brother in exchange for money is a sale. If one of the sisters denies the sale and claims it was a gift, then this matter involves a difference of opinion among scholars, whereby each party swears an oath concerning what they denied, and neither the sale nor the gift is established due to the absence of evidence. As for the rest of the siblings who acknowledge the sale, their transaction is binding. The matter requires establishing evidence and then administering oaths, which is done through a Sharia court, or by directly consulting scholars to hear all parties, based on the saying of the Prophet, may Allah’s prayers and peace be upon him, to Ali, may Allah be pleased with him: "O Ali, when two litigants come to you, do not rule between them until you hear from the other as you have heard from the first, for if you do that, the judgment will become clear to you."