Are the heirs obligated to hand over the debt amount to a non-Muslim person who claims that the deceased owes him, knowing that the deceased did not inform his heirs about this debt?

Issues of disputes are to be referred to the Sharia courts. The debt of the deceased must be paid from his estate before it is divided among the heirs. This is conditional upon the debt being proven by evidence, or by an acknowledgment from the deceased, or by the heirs' ratification of the creditor's claim. If the debt is proven by acceptable evidence, there is no distinction between a Muslim and a non-Muslim, and the age of the debt, whether old or new, has no bearing. The matter hinges on the validity of the documents, which are verified by the Sharia courts.