Some preliminary conclusions:
"A and B [...] work a lot better individually." So they probably separated while collecting firewood.
"A has OCD and can't stand things being messy. [...] There's a pile of firewood at the campsite, piled extremely neatly." So the firewood that's already there was probably brought by A.
"There's firewood under [B's] body, suggesting that he was carrying it at the time of death and fell on top of it after getting hit." B was only just bringing his firewood to the campsite when he was attacked.
"C and D are tasked with setting up the tents" and later "The tents have been set up", so there seems to be no reason for C and D to have left the campsite. Let's assume they were there all the time.
"E and F [...] pretty much can't lift more than their backpacks," so it doesn't look like either of them could have hit B with a chunk of wood hard enough to kill him, or knocked out C and D.
The campsite bears "no major signs of struggle" (or, we assume, of bodies having been dragged there), so we can assume B was killed there and C and D were knocked out there.
A and B are best friends, so we can assume neither of them killed each other.
C and D are best friends, so we can assume neither of them knocked out the other.
By the logic now stated in the latest edit to the question, G did not kill B.
We've now eliminated A, E, F, G, and presumably yourself (unless you're an unreliable narrator) as B's killer, leaving only C and D. Since they were together the whole time, they must have conspired together to kill B. The only question remaining here is motive.
Now we've eliminated B, E, F, and again presumably yourself as the person who knocked out C and D. So this must have been done by A or G. By the same logic as was used to eliminate G as B's killer, he can't have knocked them out. A also has the best motive as he was B's best friend - perhaps he saw them kill B? The other possibility is that they weren't really knocked out at all and were only faking, but let's assume your observations were correct on this one.
Now we've eliminated B, C, D, and again presumably yourself as A's killer. That leaves E, F, and G.
Apologies for the lack of spoiler tags; let me know if you want me to put some in!