I hope this message finds you well. There are two issues that I need to address relative to your question. First of, I am a USPTO registered patent attorney and deal in intellectual property licensing in the US and abroad as well as contract law for personal service. As such, this situation is not new to me and I hope to provide you with very satisfactory information.
This first issue I want to address out of an abundance of caution and because it has bearing down the line. As you know, piracy of ideas is a major problem in Asia - China in particular. As such, you need a strong non-disclosure
agreement that is pre-approved and perhaps even an attachment to the contract you sign with the US based companies. Even with the NDA, piracy is possibility, therefore the US companies should attempt to obtain, if they have not already, IP protection in the US to at least prevent importation of pirated goods into the US.
As to the second issue, you can contract with US based companies to essentially be a middle man as a reward for your services and for functioning as a Asia based liaison on behalf of the companies as issues may arise. In fact, the later part is the hook that generally makes companies desire your service and willing to sign an exclusivity agreement with you in the process.
Within that contract, you want to also address and limit any liability you may have for their confidential information being exposed or pirated. You want to address through contract language that they are responsible for their own IP protection over and above the NDA you will have companies sign through their own intellectual property protective measures.
So, the answer is that you can contract to limit the companies and make them work through you. You can place penalty provisions in the contract to benefit you if they violate the terms of the contract. You may want to make the applicable law as to contract disputes be in California, so as to stay away from Asian courts.
You need to get pre-approval for the NDA you will use and you need to be willing to work in handling issues after actually setting up an agreement between the US companies and suppliers.
Let me know if you have any other questions or comments. I want to assure you are comfortable going forward.
Best wishes going forward.