Taken literally, EP 6 is a bigger puzzle than ever. 17 people ? And how does Kanon move around between closed rooms as though they didn't exist ?
But then, even the slowest of readers should have caught on the answer to this, as the symbolism is laid on very thickly. The whole "lovers' trial" sequence has no plot purpose except to hint at it, after all. So let's spell it out clearly : Shannon = Kanon = Beato. It's only one person switching between identities as convenient. So of course they can only pledge their love to one person at a time, hence the symbolic love trials (which of course mostly take place inside their head). Thus Kanon never was in the Cousins' room ; Shannon exits the room next over through the window, and changes into Kanon (maybe because it's more convenient to run around ?) to head to the mansion ; and Kanon can disappear from the guest room by changing into Beato * (I presume Erika got a well-deserved Stake into the face when she opened the wardrobe).
The various flashbacks help explain how these multiple identities came to be. While the actual reason why remains a mystery so far, it's plenty clear that the Kanon identity was created by Genji (who can easily fake a servant's existence and arrange the shifts so that they're never seen together), with Kumawasa helping the deception (did she stumble upon it, or was she in on the plan from the start ? Who knows...). What seems clear is that nobody other than those three knew about it ; that's the only way Jessica's crush makes sense, and everyone seems to treat Kanon better than clumsy old Shannon (Krauss even taught him how to shoot !).
What's a lot clearer is how Beato came to be. Six years ago, Battler gave to an impressionable young girl a description of his ideal woman ; is it any wonder she'd decide to remake herself in that image ? And of course she'd be disappointed now that he doesn't remember this "promise"... (Also, remember that the earliest rumours about the current Beato were started by Shannon trying to cover for her own clumsiness...)
You'd think that Shannon & Kanon being the same person would be unworkable, but it actually works surprisingly well with the existing narrative. Most of the occasions when they're seen interacting together, they're either alone (so it's all in their head) or with Genji and/or Kumawasa ; the few exceptions are interesting in their own right. Let's go at it episode by episode, shall we ?
EPISODE 1
Throughout the episode, Kanon's actions are very suspect ; he's the one who finds the first set of corpses, and later who opens up the room with the second twilight's corpses. That's plenty opportunity to fudge things around. The attack against him by Beato is easy enough to fake, and his offscreen "death" was witnessed by only Jessica (who has every reason to cover for him) and Dr Nanjo (who has no credibility whatsoever at this point).
Now, this certainly isn't Shannon's corpse that Hideyoshi found in the barn. I guess it could be a random decoy corpse brought in by Shannon to fake her own death, but I don't really believe in such a contrivance. I'd much rather think that there were only five corpses in the barn, and that this was a "tactful" way for Shannon (helped by Eva & Hideyoshi, who were obviously all for it) to break up with George. I presume that at this point Beato was dominant, and she's only interested in Battler.
This, obviously, suggests heavily that Eva, Shannon and Hideyoshi killed Krauss, Rudolf, Kyrie and Rosa (3 against 4 is plausible with surprise and better weapons on their sides), and Gohda was just in the wrong place at the wrong time. I have no clue why they left Natsuhi alone... as a scapegoat, maybe ? Anyway, it's no wonder Kanon would kill Eva and Hideyoshi later on (they knew too much), and the same motive can be ascribed to the deaths of Genji, Kumawasa and Dr Nanjo later on. As for Natsuhi, it was personal : there's a long-standing grudge between her and Shannon, and a flashback in EP 6 showed that she didn't treat Kanon much better. (Also, see my thoughts on EP 5.)
Presumably the Rock Falls Everyone Dies ending prevented the conclusion of this particular story.
EPISODE 2
In this iteration, it seems clear that Shkanon made a deal with Rosa when the latter caught her cosplaying as Beatrice for Maria's sake. I think Rosa was smart enough to catch who she was dealing with, but Shannon might have been good enough for the "Beatrice" façade to work. At least she went the full yard to make it work, with Genji's help, hence the whole guest room set up. And of course Shannon and Kanon were the only ones authorized to serve "Beatrice" meals (presumably they ate the food themselves).
We know in red that Kanon died in Jessica's room. Well, since Shannon's still walking around alive and well, this can only be meant in the spiritual sense : the Kanon personality "died" when she killed Jessica *. The same thing probably happened to Shannon when it became time for George to buy the farm too. EP 6 tells us it's nearly impossible to be 100% sure of someone's death (especially with Dr Nanjo dead), and the Kanon loophole to the red text has shown us that it's perfectly possible for "Shannon's corpse" to still be alive inside Natsuhi's room (which explains the locked room : the killer's still inside).
I'm not entirely sure what was the deal with killing Kumasawa and Dr Nanjo (did they balk at the murders ?), but with Shannon and Genji around Gohda wasn't going to publicly object to the "a witch did it" version.
It's a bit of a shame that when "Beatrice" was finally reunited with Battler, he was too hammered to understand it clearly...
EPISODE 3
The first twilight is built on a gigantic lie : there's no way the parents could have really found the chained rooms as explained, considering that there can't be separate corpses for Kanon and Shannon. I'm a bit confused about how much of it is a lie : are Genji, Gohda and Kumawasa really dead too ? I'm going to say "yes" for now.
And the rotating wheel of people "Beatrice" allies herself with now falls on... Rudolf and Kyrie ! I'll admit I have absolutely no evidence on this one, but I agree with whoever's WMG that the "chained locked rooms" setup smelt like something Kyrie would cook up. The four "real" corpses and Shannon playing dead are enough to fool the other adults, especially if Dr Nanjo was strongly advised to play along.
Rudolf and Kyrie suddenly going to the mansion, ignoring all caution, can thus be chalked up with trying to meet their accomplice (Beato), but Hideyoshi tagging along and Eva tailing them leads the a bloody confrontation only Eva came out alive of. Beato was too scared to even show up, although she did retaliate against Eva by leading George away from safety, giving him a last kiss, and killing him. (There's also the option of Eva aiming at Beato and mistakenly killing George, as the witch's narrative suggests, but I'm not sure about that.)
Later on, Dr Nanjo was obviously killed by Beato, yet again using the "Kanon & Shannon are dead" red text loophole. I'm not entirely sure why she hid Jessica away from Eva, though.
EPISODE 4
I'm really not sure at all what happened in this one. Grampa showing up at the family conference is obviously bullshit, as are the captivity and escape scenes. Maybe it turned into a bloody shoot-out until cooler heads (Krauss, Kyrie and Shkanon) prevailed ? They at least got a common version out for the kids.
Most of the mechanics for the other deaths elude me. Did Jessica kill George ? How were Gohda and Kumasawa killed ? How did the other adults die ? Who poisoned Maria ? What's sure is that Beato survived long enough to have her confrontation with Battler. But then, what happened so that Battler could find Shannon's corpse later on ? Did she kill herself ?
This is the episode I don't have much clue about.
EPISODE 5
Now this one is interesting.
Let's forget about the first twilight and everyone maybe pulling a prank on Erika. What I'd rather talk about is the midnight conference. What became obvious on a second reading is that it's complete bullshit, as it shows Shannon and Kanon interacting with everyone as individuals. So they all lied. And indeed, we know that Battler's not a reliable narrator anymore, while Erika had already left the building. So something completely different from what was described happened then. It's obviously when the prank against Erika would be debated (and Rosa, leaving halfway through, would have briefed the children about it)... But what matters is that it frees Shkanon up to make the call to Natsuhi as "the kid from 19 years ago".
And I believe that's who Shkanon really is. After all, EP 6 told us that "all this started 19 years ago" when referring to her, didn't it ? And this would provide all the more motive for Beato's grudge against Natsuhi, which has been something of a constant so far.
By the way, I'm all the readier to accept this episode's proceedings as a prank against Erika because of one point : with Battler becoming the head, Beato loses a lot of her motivation to go on a murdering rampage against the family. (And she certainly wouldn't do anything to incriminate him.)
So, that's what I've managed to piece together so far. Really, it's remarkable how a single, apparently impossible reveal made nearly everything clearer. It even explains some random bits of characterization, such as why Kanon is so reluctant to give in to Jessica (their relationship is built on a big lie). That's the sign of the best twists : it makes complete sense in hindsight.