Should cheating be reported?
You should report this immediately, but be sure you collect evidence.
Edit: The reason that you should collect evidence is that you are accusing your fellow students of gross academic misconduct that would result in serious consequences. Not only will it be impossible for anyone to pursue the matter without evidence, but making baseless accusations could result in negative consequences for you.
Screenshot correspondence (if it’s in Chinese get it translated or find a native speaker among the faculty who can translate). Emails, text messages etc should be saved as well. If your university is reputable, it will deal harshly with these cases.
The actual procedure varies by institution but the first person to contact is the professor. They’d likely want to know that this is happening and would be furious to hear this. It’s quite possible that the professor is unaware, or simply unable to obtain evidence that something is going on: if everything is happening on a non university server there’s little they can do to catch cheaters.
Would anything be done? That depends on the institution, but what you’re describing is pretty clear cut. Students can get expelled and in the case of international students, have their visa revoked as a result. If this happened in my class I would do everything I can to ensure those students are punished as much as possible. The likeliest outcome is failing the class and getting a remark on your transcript.
Help make academia better and report them.