Must I compensate the heirs for the lost amount that was a debt owed to my father and which I received from them, knowing that it was lost under circumstances where its theft is probable?

If you agreed with the adult, sane heirs to donate your father's money, and then the money was lost: if you were negligent in safeguarding it, you are liable for it unless they pardon you. However, if you were not negligent, then you are not accountable for anything, because the hand of an agent is a hand of trust and is not liable except in cases of transgression or negligence. You are liable in two situations: the presence of minor or incompetent heirs, or negligence in safeguarding the money, such as your delay in giving out the charity or your neglect of it.