Is it enough to give out, from personal money, the equivalent of the value of the food, to free the husband from the sin of eating from money earned by working in a riba-based bank when his wife's father invites him?

If your wife's father has no other income besides working in a usurious bank, then it is forbidden for you to eat from his wealth and accept his gifts. This is the view of the majority of scholars. However, if he has another lawful source of income and you are unsure whether he fed you from lawful or unlawful sources, then the majority of jurists dislike this, and the dislike intensifies the more unlawful the wealth is. It is best not to eat from it to avoid doubtful matters. What you spend from your own money in exchange for eating at his place does not remove the sin if his wealth is unlawful. You should advise this man and be cautious about eating at his place.