Why would it be illegal? IF the trainer is not driving but on duty or sleeping in the passenger seat with no intentions of driving, he doesn't even need to log.
So he's supporting 4 guys, 10hrs driving each, on a rotating shift? Even two guys on a 10hr rotating shift.... How's that work, exactly?.... I don't have to log, but I can be awake for 20 straight 'supervising'?.... What are you trying to say, Ridge, or how?
Only way I can see it is if we in one of those big studio rigs that do like trade shows look like someone can sleep on the floor in one of those but 3 men in a double bunk truck longer than a weekend it's definitely some spooning going on