[Enrique]

The two guys Chigurh killed at the drug deal weren't necessarily working with the guy who hired harrelson, but he gave them the device, which could have been done at a cost (selling it).
Anyway, in this thread people have commented on those questions you asked, in particular with respect to the person that hired harrelson. GTL commented on it and if I recall correctly, he said the book wasn't very explicit about that guy.