Charlie is portrayed by Jennifer Sky (now goes by Jennifer Band). Previously, she portrayed the Amazon Amarice and Cleo.
Also mentioned above, Danny is portrayed by Stephen O'Reilly. While he does do some acting, he is most known as the lead singer for the band Tammany Hall NYC. (Yeah, you know the "Always On Sunday" song that plays on HBO and "Wait For You" from Sex and the City? That band played those songs.)
First off, Bradley Cooper, at that point in time, played nice guy roles such as the aforementioned Will. Here, he portrays Travis. He ends up being one of the main people in The Company. To put it lightly, they certainly were the ones who did all the twists listed above.
Secondly, Sean Cw Johnson, as mentioned above, plays nice guy/heroic characters like Carter. Here, he doesn't seem to portray against type at first, as Matt is a nice guy despite sharing a creepy story in the beginning of the film. That is, until he suffocates Charlie and beheads Rex. Oh, and he also attempts to kill Emma. Also, in a deleted scene, Matt drives Danny to commit suicide.