As far as father's liabilities or debts are concerned, you or your property are not bound because of avyavaharika debts(that are taken for illegal purposes)So,son's pious obligation(the liability of sons to pay their father's debts as his heirs) is not applied in your case since father indebted not for legal necessities but for gambling,etc and therefore you or your mother are not severally or jointly liable to repay it by your person or on your property.
Thanking you,