Not all their food is najis. If their food is dry and they have not touched it with dampness, such as nuts or fruit, then they are not najis. You do not have to inform him of such a law. It is better to deal with him nicely and avoid dealing with such an issue.
Istikhara is not obligatory but it was narrated that it is used when there is doubt in the personâ€™s mind. Istikhara for marriage when the conditions are met does not correspond to what is reported in the narrations about accepting a person for marriage when the conditions are met. Yes. It is better to seek the goodness from the Almighty and depend on Him.
If the time of dower payment is due then it must be paid in full when the wife asks for it. The husband does not have to pay it on time if the wife agrees to delay the payment. Also if the husband is unable to pay it, then it is permissible for him to postpone the payment or part of it.