Legal Question in Personal Injury in California

There is no tort of "negligent exercise of retained control." You have to prove violations of the law of Guatemala, and that the person or entity you want to have held liable was in actual control of the conditions and/or conduct that violated the law. It seems you are trying to have the California firm held liable for nothing more than being a major customer of a factory that engaged in illegal activities. That isn't even close to enough. You keep using the words like "influence" and "knowledge." I don't know Guatemala law, but in the U.S. that is so far removed from what it takes to establish liability that the NGO would risk being sued for malicious prosecution and abuse of process after the CA company got the case thrown out. Knowledge and influence is not legal control, and there are no US laws that would help you. Furthermore, in the U.S. you can't use an arbitration tribunal without the consent of all parties, either in a contract that calls for arbitration of disputes, or by an agreement to arbitrate a dispute once it arises.