Episode 2:
Possible culprits: Rosa, Jessica, Eva, 19th person, Genji, or combinations of them all. I do think that Rosa is definitly involved, though. And I don't think Eva survived the first twilight, but that she was possibly a "Beatrice".
No matter how I look at it, I definitly think Rosa is involved someway.
Let me start with the pre-conference stuff. Shannon and Kanon's Beatrice.
My biggest theory on this is that the Beatrice is Jessica or Eva, or maybe both. Although, in all cases of pre-conference, it means that Eva would need to be on the island, and I doubt she could just sneak in. There's also a possibility of delusion.
The first time we see her is infront of the portrait. This could have been delusion, as Shannon was hungry and in a daydream, and I think Kanon might have decided to not eat as long as Shannon didn't eat, so he was also suffering. In fact, Kanon didn't know who was torturing Shannon until Shannon said something. Not who the person was, but the way she spoke and the portrait being there might of had some effect.
Then there's the Jessica possibility. It's interesting to remember that Jessica is the only person of the 18 who has blonde hair, like Beatrice. Once again, I'm split on possibilites on this. Either Jessica toke on a "Beatrice Personality" to try and encourage Shannon with magic, or Jessica was just trying to encourage Shannon as herself, and was just teasing her (all the apprantly "mean" comments. Shannon was also being pretty mean to Jessica as a form of teasing, such as "…それはそれは肩身の狭い思いをなされるでしょうが、卒業までの短くも長ぁい間を耐え忍ばれるだけでござ いますし。愛し合う恋人同士にとって、独り者の僻み顔が何にも勝る甘ぁい蜜なのです☆")
Now then, Eva is suspicious aswell, because she would obviously want to try and discourage Shannon, with the whole "George is meeting someone who is much more fitting then you" dialogue, and she might of expected Shannon to not break the mirror, thus Shannon would feel like she could never get into a relationship with George.
The second time we see Beatrice is during the Beach Tea Party. I have trouble seeing Eva get so friendly with Shannon, but there might have been a reason. Possibly to hear the details of her and George's relationship and find a weakness in it.
As for delusion, maybe after the first delusion, Shannon possibly saw Beatrice more often, as she was the mediator in her mind. Kanon saw Shannon talking to herself, apprantly, but since he had also seen the delusion, he might have saw "Beatrice" aswell.
Jessica I find most likely here, as the conversation was as if it was between two friends
The third time we see Beatrice is after Kanon's rejection of Jessica's love.
Kanon could of delusioned this, because of the state he was in.
Jessica could of ended up doing this because of how heartbroken she was. Jessica and Kanon were talking about having "more than one personality" before this.
Eva would of loved to have done this.
There's also a chance that all of these were Rosa who grew a "Beatrice Personality", but much like Eva's situation, she would of had to been on the island at these times.
Now for during the conference. Note that by "see Beatrice" I mean that the person saw them but wasn't killed.
Maria and Rosa's Beatrice: One thing to note is that Maria says she has been seeing Beatrice on this island for more than two years. The two people who could easily do this, and work with my theory are Jessica(She created a Beatrice persona to help Shannon and so she also ended up protecting Maria's dreams by being her Beatrice.) and Rosa(She might have created a Beatrice personality to gain the affection of her daughter.) Maybe Rosa and Jessica are working together. It could of also been Eva who was working with Rosa.
Anyway, those are the two people who I see as "Beatrice" here. This is one that I can't see as a simple delusion.
Kyrie's Beatrice: If it was Rosa, Eva, or Jessica taking on a personality of Beatrice, I think Genji would treat them as Beatrice, for the sake of Kinzo. And, specifically if it was Jessica who was dressed as Beatrice, Kyrie might have seen her as Beatrice.
Honored Guest Room: This makes it obvious that this Beatrice is the same Shannon and Kanon saw before, or maybe another person working with the one before.
Also, there was a scene where everyone asks Genji who this "Beatrice" was, but before we see Genji's response it cuts to the next chapter. The only people who heard his response were the 6 who were sacrificed in the first twilight, Rosa(The supposed culprit, in my theory), and Genji(Who once again, might have not said anything for Kinzo's sake, or he might have not known Rosa was the one who was killing everyone.)
First Twilight: Victims: Krauss, Natsuhi, Eva, Hideyoshi, Rudolf, and Kyrie.
First thing, before the first twilight, the victims and Rosa, and Beatrice are seen in the chapel, but I don't believe this scene was really as it was shown. I think that Rosa might have discovered the gold and gotten all her siblings who always looked down on her to admit she was smarter. I can't think of a plausible situation with Eva and Jessica where they would admit that "Beatrice is a witch" unless Rosa and "Beatrice" threatened them.
As for discovering the twilight itself, I find it completly implausible that Rosa could of reasoned that the key to the chapel was in Maria's envelope. Maybe if she had held the envelope, but she never did.
Secondly, we see a letter left on the table. This is the letter that is suppose to be read at dinner, as Beatrice's introduction, however, it never was. The person who got this letter was Rosa herself.
And thirdly, Rosa NEVER mentions the events in the chapel from the previous night, even though she was apprantly with them.
Also, I would like to note that after Shannon's talk with Beatrice, we never see Beatrice anymore from a living person's perspective who lives to tell about it, until the chapter before the endscroll, which I'll explain later. Explanations for why we never see Beatrice based on who Beatrice is:
Eva: She is dead, so she is never able to act as Beatrice.
Jessica: Either because she died at the second twilight, or because she "died" at the second twilight. By the latter I mean, she faked her death, then assissted Rosa in killing others, so she wouldn't want to show herself to living people.
Rosa: She only goes into Beatrice personality when she is going to kill the victims.
Not to mention, how much the whole scene seems dead-set on making Maria happy, with the whole "Happy_HALLOWEEN_for_MARIA"
Both Rosa and Jessica could have easily taken the key from Maria's envelope.
Second Twilight: Victims: Jessica and Kanon
Rosa could have done this when she got a gun. I know that makes the scene out of place with the killing in terms of time, but we have no guarentee it happened when Beato said it did.
Also, it would have been easy for Jessica to kill Kanon here.
Points that make Rosa suspcious: She was the one who found Jessica's key. Possibly she use the key then carried it with her, then pretended to have found it(She accused Battler of this with Beatrice's last letter.) Also, she seems really desperate to blame one of the servants. And, the golden butterflies that landed on Rosa's back when she went to inform Kinzo.
Points that make Jessica suspcious: She was never proclaimed dead in red. She could easily lock the door from inside.
Side Note: I noticed that when they discussed there being 3 gold bars when there could only be 1, Gohda says he toke everyone's luggage, but if you recall correctly, he didn't take Rosa's.
Seventh and Eighth Twilight: Victims: Kumasawa and Nanjo
Kanon is the most baffling part here. If it was as simple as "Kanon killed everyone", I wouldn't trust this scene, as I don't trust most scenes seen by dying people or the person I think is the culprit. However, Genji, Shannon, and Gohda saw it. They never really confirmed the supernatural happenings, but they did confirm they saw Kanon. There is a possibility they got bribed or are really part of it, but I'll work on the assumption they aren't.
For one thing, Kanon ends up speaking in a similar way to how Rosa did in the First Twilight ("……ずぶり、ぬめり、ごぷり、溢れて。")
The most probable person here is Jessica, though possibly Rosa(though unlikely). It's rather gorey, but it's possible that she cut off Kanon's head and put on his clothes, or she cut off the skin of his face and "wore" it. (If this is true, the Tea Party might have some symbolism in it.) Also, Kanon's corpse was never found, so we have no idea if it was mutilated, as I say. Whoever it was, they probably hate spiders with a passion.
The rest can be Jessica killed them, still disguised as Kanon and escaped.
Then the corpses disappear. Using a similar explanation that I've used in the first and second twilight: Someone moved the two corpses, then left the master keys in the letter, leaving it in a secret place where Rosa would be able to find it. Rosa picked it up while they moved to the servant's room and then pretended to find it.
Fourth, Fifth, and Sixth Twilight: Victims: Gohda, Shannon, and George
This is pretty easy to explain. Jessica was easily able to kill them. I think the fact that Beatrice got mad at Shannon seeing love as more than just lust points to something tragic. Maybe Jessica thought she had a boyfriend, but it was actually a one-time thing for the boy? Or if the culprit is Beatrice, it might hint at Kinzo doing something.
I'll just point out again, I don't think the paranormal stuff is truly happening, if there is noone who survives to tell of it. I think it's close to what happened, but not exactly it. It'd be easy to block the door, if the person who killed them heard they were planning on going to Natsuhi's room.
As for the whole closed room aspect, I'm going to go with what I've been saying before. Secret spot, Rosa picks up the key, etc. I know I've repeated it, but it being repeated isn't that suprising, esspecially considering that everytime it's Rosa who finds the keys.
Beatrice's Final Letter: Rosa could of easily placed this letter twice. One, when she checked the room right when they left and again when she was checking the room when she came back.