Mr. Bagwell makes a good point, and raises a broader point: When dealing with potential controlled/affiliated/management group scenarios in closely held businesses, make sure you have all the facts and ask all the relevant questions as it relates to family attribution. For example, while it would appear based on the facts you provided in this post and previous post that a controlled group does not exist, as Mr. Bagwell points out, if the husband and wife have a minor child (under age 21), all bets are off:
Each spouse's 100% ownership in their respective companies is attributed to the minor child. The minor child is deemed to hold a 100% interest in both companies making this a classic brother-sister controlled group of corporations. This means that the controlled group cannot offer both the 401(k) and the SIMPLE IRA in the same year.