Is the father included in the meaning of the Hadith: "and his food is unlawful... how then can his supplication be answered," with his continuation of paying off an interest-based loan after his repentance, and will his charity be accepted, and will the supplication of his children for him be answered?

Usury is a grave sin, but sincere repentance erases its sinfulness. If your father repents from the usurious loan, Allah will accept his repentance and will not hold him accountable. Your father's supplication, or your supplication for him, will be answered if the conditions for acceptance are met. The usurious loan does not affect his charitable giving or his good deeds, because it is a debt upon him, and there is no harm in his benefiting from it or giving charity from it. It is not necessary to hasten the repayment of the loan unless doing so would eliminate or reduce the interest.