1) There is truly nothing you can DO to STOP them from using your identify in the current manner. The best you can do to impede them is to essentially "cyberstalk" them and report their every attempt to defraud someone to the system administrator or security team of the website they use to do this. So essentially hit the 'Report Abuse' link.
It gets hairy here. It's now a he-said she-said situation. To put some weight behind your claims, and as recommended as one of the steps to take if you are a victim of identity theft, you should to file a police report to substantiate your claims. You can do that in their state & country and/or in your state & country. The laws within the U.S. do not completely cover situations of this nature, so I would not expect the laws in that country to be so much more ahead. Moreover, realize this is now an 'international incident'. So the agencies pathways to handle this are probably not established. (When my ex had their credit card # stolen and recreated, while they still had the physical card within hand, the police agencies of both states were not equipped to handle this situation. Filing a report was like inserting ourselves into a pinball machine.) And a situation of this nature, crossing country lines, is probably not high on InterPol's to do list.
2) Yes and no. While there is a lot of information on the 1st page of your passport. The thief now has a clear picture (you mentioned photos in addition to the passport copy), your full name, D.O.B, state of your birth, your passport number and possibly a clear signature (if you copied the 1st two pages). While this alone is not enough for ID theft, it's working framework for the scam artist to build a case up around. They now have your email address and depending on their sophistication they can start to try to search for the other pieces of your ID puzzle (16 big pieces listed below).
While it seems like their motivations are not as lofty now, you could be an addition to their database for further mining. It might be best to take some precautionary steps. A good website for ID theft information and actions to take if you are a victim is: https://www.privacyrights.org/identity-theft-what-do-if-it-happens-you
Be sure to save your documentation of the incident (email exchanges, reports you filed, requests you made to credit bureaus, etc). Just continue to monitor your credit like you should normally be doing www.annualcreditreport.com (the only site authorized by federal law).
If any of your accounts (esp. the email account you used in the exchange) have a password that uses information on that passport page, or any other information you make have sent to this person, change it immediately.
As it relates to the harm of others, there is nothing you can do other than put out a public-service-announcement-of-sorts on the websites that the scam artist is listing on.
Good luck to you. Just keep your eyes open going forward.