Is the amount claimed as interest, resulting from the delay of the questioner's father in paying installments for a house he sold before his death, considered a debt that his heirs must repay, especially since his father was unaware of this claim at the time of sale, and the claim emerged years after his death?

We ask Allah for mercy and forgiveness for your father, and we advise you to increase supplications and charity on his behalf. As for the usurious interests imposed due to delayed installment payments, they are not a debt owed by your father, and you are not obligated to pay them. This is because they are prohibited usurious interests, which are impermissible to impose or to commit to. If such an imposition is placed upon someone and they are able to evade it, there is no sin upon them, as these impositions are unjust and oppressive.