First you say multiple companies of which the client is 100% owner, and then you say just two, with the client owning 100% of one and 50% directly of the second. This is as I understand you. Facts actually matter, so gather all the facts. Then, if necessary, read the controlled group code and reg provisions, including the attribution rules. You may need to dig into other IRS "guidance" and the case law. This could be a very messy situation, but hopefully not.