I think that you're onto something. Spoilers and theory:
Something about Chris just seems off. Especially with how Russel refers to him as a kind of "back stabber/traitor" and how he wants to "protect Ben from Chris". Something felt off about the whole forrest scene too. I think that either you are right about Chris or that he is the murderer because so far he has been at the places where the murders (that we have been there for/know more about) have taken place (the restaurant and the place with the forrest for the trip (I even think that it was mentioned that Chris left the group at some point during the dinner while Ben was sleeping, which makes me even more suspicious of him and Ben's "hallucinations").