What are the legal implications for the the heirs after the annulment of a real estate sale agreement that was agreed upon and signed, but without any payment being received, due to a dispute among the heirs over its sentimental value?

If the sale contract is concluded with offer and acceptance, and the two parties to the sale depart from the session, then the sale becomes binding and it is not permissible to revoke it except by virtue of a conditional option, or a defect, or egregious deception.

The sale is binding by the contract and the departure [from the session], whether the down payment or the price has been paid or not. It is forbidden for the seller to refuse to hand over the property, and he may invite the buyer to annul the contract.

It is permissible for the buyer to request money in exchange for annulling the contract.