Is it permissible to eat from the food of my fiancé's family, knowing that his father works for an Egyptian insurance company and will help him with the wedding expenses?

If your fiancé's father possesses lawful money in addition to what he acquired from the insurance company, then it is permissible to accept his gift, though it is disliked. The degree of dislike increases or decreases based on the proportion of unlawful money to all his money. However, if all his money comes from the insurance company, then it is not permissible to deal with him or accept his gift except in cases of necessity. There is another opinion held by some scholars that permits accepting maintenance and gifts from someone whose money is unlawful due to its acquisition, not its essence, such as dealing with usury. This is unlawful for the earner, but not for one who takes it rightfully, citing the Prophet's (peace be upon him) actions with the Jews as evidence.