Paying off one’s parents debt:
A child is not obligated to pay off his father’s debt, unless his father has passed away and he has inherited money from his father. There is not even a Mitzvah involved in using his own money to pay it off.
 Admur C.M. Mechira Halacha 7; Michaber C.M. 107:1; Hagahos Ashri Kesubos 9:14; Smeh 107; Gilyon Maharsha 240; Pesakim Uteshuvos 240:32