Is it permissible to eat at the house of a person whose earnings are lawful, but whose wife's earnings are unlawful, knowing that the husband is responsible for the spending, or should the possibility of the commingling of the two types of money be taken into consideration?

If the food is from the husband's or wife's lawful (halal) earnings, there is no impediment to consuming it. However, if its source is from the wife's earnings, and her lawful money is mixed with unlawful (haram) money, then if the lawful portion is predominant, there is no impediment to eating her food. But if the unlawful portion is predominant, then consuming it is disliked (makruh).