Writing

OP's top comment isnt showing up here, so I'm copy-pasting it here:

Here's my gripes with each name:

1. In my story, the kids go to a fantasy boarding school, get sorted into four different houses based on their beliefs, and through great temwork overcome a secret bad guy. If I name my magically-talented male lead Harry, I think J.K. Rowling might personally come to my house and shoot me.

2. Garanhir was kinda picked out of a hat of mythical names. I like Terry & Minty, though

3. Naming my edgy Kaiba-alike "Adolf Kills-King-Arthur" might be a bit on the nose

I like a name that can be broken down multiple ways to convey things about tone and relationships dynamics beyond the binary divide of formal name and nickname. Indiana Jones jumps to mind; practically no two people in a movie call him the same thing. He's got two different titles, a given name, a surname, a chosen name, a diminutive of the chosen name, and whatever you call the category "Junior" falls into. And no two of those names or name components have the same mood when you hear them next to each other out of context.

I look at Harrison Bach up there and I'm feeling like, out of this cast, he in particular doesn't really give you that freedom to play. Harrison and Bach are equally easy to say, equally serious sounding, and Harry is like the least informal classical nickname. But it is cute that him and his best friend have rhyming nicknames. Me liking the Harry part of it in particular but in light of your discomfort with his sharing the name of Harry Potter, maybe change his given name to Laurence and nickname to Larry? You preserve the rhyme and now all three of his names have a significant tonal difference from each other.

Terry is great, no notes.

Minthe and Minty sound almost exactly the same as each other, so I don't buy Minty as even being her nickname. Minnie or Thee could work better as diminutives but might I suggest breaking the mold here and giving her a nickname that isn't derived from her name at all? I don't have a suggestion for one, though, not knowing anything about the character that might have inspired a nickname.

Adulphine "Alfie" Mordred. In terms of that Indiana Jones factor, these are the three most sonically different names any of these characters have and I love that for her but you're not wrong about it being kind of a lot. The question isn't really whether it's right to be kind of a lot in a vacuum, though, it's whether it makes sense for this character's name to be kind of a lot diegetically.

This curse she carries, what's the nature of it? Is it because she comes from a family of evil aristocrats? Because I have to assume any Mordred who willingly names their kid Adulphine has to be one, even without those names having associations. Frankly, if I met an Adulphine Mordred in real life, my first thought would be "vampires are real" before I registered what other famous people/characters those names sort of/do belong to. If the curse is supposed to be bad luck that could have happened to anybody and her origins are otherwise unassuming, you gotta go back to the drawing board and give her the most incognito formal name out of the whole crew with only an evil-sounding nickname, and a recently-acquired one at that.

Feel free to ignore me but:

Alfred "Alfie" Joseph

Bengiman "Bengie" Oliver

Maya Oliver

Persephone "Percy" Elm

• in greek mythology Persephone was taken by hades (in an unwanted arranged marriage of sorts arranged by her father zues) to control the underworld with him, becoming the queen of the underworld. her mother sad to lose her causes winter and apon Persephones return to her mum every year, summer returns.

Also

"The myth of a goddess being abducted and taken to the underworld is probably Pre-Greek in origin. Samuel Noah Kramer, the renowned scholar of ancient Sumer, has posited that the Greek story of the abduction of Persephone may be derived from an ancient Sumerian story in which Ereshkigal, the ancient Sumerian goddess of the underworld, is abducted by Kur, the primeval dragon of Sumerian mythology, and forced to become ruler of the underworld against her own will." Wikipedia

I also like the name lucida

These are just random names that popped into my head just before sleeping so feel free to ignore or pluck what you like (also I spent way longer thinking about the first names then the last names so I'm not set on my last names)