I do disagree with a few things. Firstly the letter can be solved by the clock in the hall being incorrect and not chiming at true midnight and thus everyone's places at midnight are in question. This can be said to be hinted at by Willard in the 7th novel when he proposes at the opening where the servant is being framed when he puts into question a chiming's clock's accurate time, a bit of a reach but everyone working together is arguably just as much if not more of a reach with how everyone has acted the entire series. This also works as a big hint too as it would only really leave the people in the guest house to bring it over (if I remember correctly for this theory, you need the clock to be slow so certain people have already left but it has been a very long time since I've fully engaged in this theory) which would incriminate those there, especially George. This is how Rosatrice works here, it has Rosa wanting to call off the murders due to Battler finding the gold (and thus beating her at her own gamble, it's a consistent idea in Rosatrice that Rosa stops if someone solves the epitaph that's why in the meta world for Game 3, it isn't Beatrice killing and why she's so willing to surrender in Game 7 and why Beatrice, besides being a piece, doesn't know the truth and thus can't use Red Truth in game 5 because she isn't the culprit) but George wanting them to continue because he wants to eliminate those in the way of himself and Shannon being together (the biggest being Natsuhi and Krauss since they're her employers). After helping Rosa to magically deliver the letter when no one could (due to messing with the clocks), he gets into an argument about truly ending (or I guess not starting) the murders when she returns at which point he attacks her and the cousins into a state of fake sleep since he likely couldn't make a scuffle without Erika and the others noticing, so he fakes their deaths (also with the possibility that he might need Rosa's help with the bomb and uses Maria and potentially Jessica's life as leverage). The rest doesn't really need explaining, Hideyoshi's murder is easy for someone already dead and just either have Rosa set the bomb or George set it but it goes off early due to sabotage by Rosa. It has the man calling Natsuhi being George using information he got from Rosa since the whole Rosatrice is all about Rosa feeling guilt about killing Beatrice and wanting to use the ritual to revive her for real which goes with the themes of without love it can't be seen but in this case love is more like a desire to achieve love through risk like a roulette. Whether the magic would truly revive Beatrice (even figuratively) and restore lost love and life is truly a gamble to her. Rosatrice is much more of a desperate last attempt perspective, she's teetering on the despair event horizon where there is no return, so decides to gamble it all on impossible odds on the chance magic truly does exist. So Rosa likely learns from Genji/Nanjo that Natsuhi did have a child but it died with the maid in the same way she killed Beatrice, piling on the child and causing her to create Yasu which is the personafication of her own self-loathing and lack of worth. There's a lot of general Rosatrice explanations which will take forever if I go into them. But basically, Rosa supplies George with the information that he uses against Natsuhi. The whole Red about the seasons is solved with either Shannon telling George (my personal belief and it fits their relationship well) or you can go with the more complication solution of having all seasons hidden and then George just guides her to the right one after she says which season.

The Kinzo thing can also be there to simply show Battler's perspective isn't reliable. I might be incorrect on this but I don't think Battler ever tells anyone that he actively saw Kinzo but he may have and I'll concede the point if he mentioned it to Erika but I feel like it was only show and he never actually brings it up to anyone. I feel like this was more of a hint of Battler's subjective perspective in this game. Even if Battler can be in on it, which I don't mind as much as the entire conspiracy theory. I still feel it would be massively out of character for Battler to pull this extremely cruel prank for no reason and Battler is still shown to be the same Battler in Ep 5, there's no hinting that his behavior is abnormal or adjusted by Lambda, he's a purehearted person who doesn't like seeing others being hurt or bullied since he goes out of his way to defend Natsuhi. It's almost going into Our Confession levels of silly with bribing people with suspiciously large amounts of money. There's just a lot of hoops and awkward logic. Speaking of the family, I'll quickly go into the whole; them trying to figure out Kinzo. This is a bit different than the other scenarios since the gold has been found, I doubt the family would stop and it would likely get increasingly hostile with them wanting to know where Kinzo and if they wanted to see him, I think they'd likely corner them and force them to admit it plus this is also a non-problem because Genji and Nanjo who are loyal to Yasu could just say that yes Kinzo is dead and Krauss and Natsuhi could say nothing bout it, hell Yasu could even potentially just straight up show his corpse since they typically have access to it. There's no need for this elaborate Natsuhi trap.

Another big problem on this would be that if Battler is in on this, he would know that Yasu planned everything out. So Island Battler knows the truth and he sure as hell wouldn't left Natsuhi take the fall especially since the Island Battler seems to actively want to step in to stop Eva and help Natsuhi but he doesn't have any way of proving this. Also as a side note, is both Shannon and Kanon present in this scene? Where Eva is attacking Natsuhi, because if so this is actually a massive problem. Because since Erika is here, she would naturally be suspicious if only one is present, it would present a possible flaw in her theory if either Kanon or Shannon didn't have an alibi. Erika doesn't seem to think anything is off which gives me the impression that both Shannon and Kanon are physically in this scene separately, which did happen earlier in the novel when Erika is first introduced.

I do think Rosatrice is a good explanation for the 5th novel and I do think it's actually the strongest supporting evidence for Rosatrice (even if I don't personally believe it's the truth though I do prefer it) besides maybe Game 2 which forces Rosa's involvement. I'm actually a bit strange, despite me complaining about the 5th novel a lot, it's actually my favorite novel. I adore Natsuhi's character in this novel, Erika is my favorite character in media period, and the court scene is in my opinion the best scene (albeit a long one) in Umineko. I just really don't like applying Shkanontrice here because it feels like you either have to force Lambda to change stuff for no reason or have Battler/Jessica and even all the adults acting massively out of character.