Does the deceased's father still owe a debt to the Real Estate Development Fund if he sold a mortgaged house and agreed with the buyer to pay the remaining installments, then it became apparent that neither the buyer nor the subsequent buyer paid the debt in full, knowing that the deceased's father reduced the house's value by an amount equivalent to the remaining balance owed to the Real Estate Bank at the time of sale?

The majority of jurists hold that a mortgage (rahn) is not binding unless possession is taken. If the mortgagee (the bank) has not taken possession of the mortgaged property (the house), then it is not binding, and the mortgagor (your father) is permitted to dispose of it by selling it. However, in the case of a mortgage to a real estate bank, there is a condition that the mortgagor may not dispose of the house, and this condition is binding and must be fulfilled. Sheikh Ibn Uthaymeen holds that it is not permissible to sell a house mortgaged to a real estate bank for two reasons: the existence of the condition, and that the mortgage becomes binding without possession being taken. If the sale takes place and the house comes into the possession of another buyer, the sale is valid according to the majority of jurists, and no blame is attached to your father as long as he has deducted the amount of the debt from the price and did not intentionally try to evade it.