Some preliminary conclusions
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- "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**.

Main logical argument
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We've now eliminated A, E, F, G, and presumably yourself (unless you're an [unreliable narrator](http://en.wikipedia.org/wiki/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. For their motive, I quote from [Duncan's answer](http://puzzling.stackexchange.com/a/10440/5373): "B must have been the one to scream 'I'm going to kill you' in the first argument and we know that C and D work to prevent violence. Being smart, they must have figured that one death is better than 2 deaths." More specifically, **D** must have been the actual killer since (s)he's the one without red hands and the only red you found on the log was blood.

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. E and F are the ones with a motive, given the earlier quarrel. They were together all the time, and their task was picking berries. So it would've been easy for them to corner A near the stream, kill him with raspberries, and then return to the campsite and scream.

Summary
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>! **D** (accomplice: **C**) killed B with a log, in order to pre-emptively stop him from killing E and F. **A** attacked and stunned C and D in a grief-fuelled rage. **E and F** killed A with raspberries, motivated by their earlier quarrel.