How can a father be kept away from resorting to usurious loans to secure his future and the future of his children, after he has spent his life in lawful work, especially with his advancing age and inability to continue his physical labor, and with the limited means of his children to help him?

If your father is indeed dealing with usury, then it is your duty to advise him to abandon usury and to explain that it is one of the gravest sins. You should also explain that usurious gains are not permissible to benefit from; rather, they must be disposed of by spending them on the welfare of Muslims or giving them to the poor, and he should only take his principal.

However, if you fear that he might deal with usury in the future, then you must supplicate for his guidance and success. Remind him of his virtue in raising you from lawful earnings, and that he is not obligated to spend on you now, especially given his poverty and need. If he insists on it, then advise him by clarifying the heinousness of the crime of usury.