I would inquire to both owners one on one and see what they have to say first and foremost. As commish, I would want to determine the sequence of events, who offered this trade to whom would be the bottom line. My first guess was that it is the same person owning both teams, but I've been surprised before, sometimes you just have a reckless owner on your hands. If that is not the case and you know it, then the owner dropping these players and clearly letting him/herself get swindled, owes an explanation for these actions either to you as commish, or the rest of the league. I would expect nothing less. I'd also keep a block on both teams ability to trade and make add drops until you hear from them again and determine what they were thinking, how this went down, etc.
I wouldnt say anything to the rest of the league until you've heard back from these two owners, assuming you do pretty quickly.