(a) Heirs are not liable for the debt of their ancestor or creditor unless it appears that the personal assets of the deceased were insufficient to discharge it, or that after due proceedings the creditor has been unable to collect the debt from the personal representatives of the deceased, or from his next of kin or legatees. If the personal assets were sufficient to pay a part of the debt, or in case a part thereof shall have been collected, the heirs of such deceased person are liable for the residue.
(b) Subsection (a) of this section shall not affect the liability of heirs for a debt of their ancestors where such debt was by his will expressly charged exclusively on the real properties descended to such heirs, or where such debt is by the will expressly directed to be paid out of the real property descended before resorting to the personal property.