1) I don't have any opinions on the specific details of any murder. But after thinking about the Mystery Genre, TL;DR: for a bunch of reasons, a high-magic explanation for the murders would make for a very unsatisfying conclusion to a mystery in almost all circunstances. Though Umineko obviously isn't playing the genre 100% "straight", I believe it does still want to deliver a conventionally satisfying conclusion to the muders. So my guess is it's most likely gonna be minimum magic "how".

2) As for "why", I want to believe it's because Beatrice gets turned on by murder. (probably something to do with love idk)

3) I think this game is working with two separate layers of diegesis. So in World/Layer 1, there's the island where the murders etc happen. My minimum magic opinion applies to 1 only. World/Layer 2 includes both Tea scene, the ??? scene and all the game elements like menus and character bios.. The player is a part of Layer 2 - though they are treated as an "outside entity" rather than a 2-native. Many seemingly "4th wall breaking" things can be given alternative explanations, but the Rika-look-alike talks directly to the player in ???. There are probably still 2 or 3 2-characters (should they all be called witches? what's the definiton of a witch?) still to be introduced too.

4) Beatrice can exist in both 1 and 2, and has been able to from the beginning. Apparently ever since Ep 2, Battler can as well, as he talks to 2-Beatrice in those conversations. But there seems to be a high degree of "not-sameness" between 1-Battler and 2-Battler, as the player (and thus 2-Battler as well, I presume) is shown a lot of into 1-Battler cannot know, and so they cannot share one consciousness. 1- and 2-Beatrice seem to have a high degree of sameness though.

5) If Battler can be in 1 and 2 at the same time, and not the same brain, this leads to questioning the nature of World 1 itself in Episode 2. It's possible that the World 1 in Episode 1 was the only "real one" - what we have know is a virtual reality of sorts, a pocket dimension created within World 2 for the sole purpose of Beatrice playing "chess" against Battler's spirit. The lead up to Ep 2 makes it seem that way. However, this would imply that all the 1-characters here are also fakes, highly advanced AIs but not human players. I don't like this because it means that nothing that happens here really matters, and even from the purely game/battle pov, a game with AI instead of humans cannot be said to be a True Battle. Maybe Ep 2's World 1 is just an alternative timeline version of Ep 1's, but with equal "realness" and human players. 2-Battler's observing never seems to directly interact with anything in World 1, so there's no "two of the same person" problem.

6) The chatting with George, Jessica etc in the first Tea scene was rather interesting. They seemed to be their own character, but having already understood and come to terms with everything that happened and offering "looking back" commentary. But no one gets over that much stuff so fast. (I've been watching some anime seiyuu radio videos on YT). Another option is that they are actors. After the play is over, they record an "extra" where they're still wearing their costumes and acting mostly in character, but with the 4th wall (or in this case the wall between Layers 1 and 2 of diegesis) completely removed, they comment on the happenings of the play, again from their characters pov. That's an interesting thought, but I don't really know where it leads.

7) Layer 2 contains the character bios, so when all of them got updated after the Episode 1 deaths, that's a 2-character talking. But who is talking to who? From the content of those messages in the first batch, it seemed a lot like Maria was talking, though later messages are a bit less Maria-like, but they're mostly Maria-like. The bio text when you "execute" Beatrice when replayed Ep 1 is obviously just Beatrice talking to the player. However, I wonder how much access Maria has to 2. One option is full access, that's why she knows so much about witches and stuff, and that's how she wrote those bios. But I'm taking the low % play and will claim that she has very little access to 2. It seems like Beatrice needs to show up in 1 to talk to Maria, and they haven't talked that many times. The char bios could have been written by a witch roleplaying as "crazy Maria". As for to who they're talking, there's a mix of to no one (just making observations), to the player, and one of them (Hideyoshi - how do you explain this murder?) to Battler. (or maybe the player to shares Battler's opinion here).

8) If the theory is that all game elements like menus etc are 2-diegetic, what is the VN itself? That is, how do we make sense of Battler or Natsuhi printing their first-person narration on the screen? What about the scenes with no first-person narrator? And the sprites showing up and the music playing, and the episode structure with a main menu linking them? It's possible that I've gone too far here, and that these questions require no diegetic explanation, in the same way they don't in any other VN - and the only game element that we should be looking at is the character bios. That seems like a weird inconsistency though, because char bios aren't any more or less gamey than the rest. Maybe everything the player sees is a 2-character (still unrevealed) communicating directly with the player, or multiple. Though this would open door for unreliable narrators, which can be either really good or really bad.

9) It also says "You may perform witchcraft to jump forward in time" when replaying Ep 1. Does this mean Beatrice or some other witch has time magic? Is the player a witch??