Would these honorifics be accurate/realistic?

I'm currently writing a story set in Japan, and I want to make sure that the honorifics I use fit the characters. I apologise for the length ahead of time.

Ami is a 14 year old girl whose parents are incredibly wealthy and high-profile. She's friendly, a bit clingy, confident, pushy, and wants to be seen as cute and respectable. She calls her best friends [shortened version of given name] -chan (ex: Hanako Yamada becomes Hana-chan). Female classmates are [given name]-san, male classmates are [family name]-kun. She becomes part of a magical girl team and I'm not sure if she'd call her teammates (who are all girls) [family name]-san out of politeness, [given name]-san like her female classmates, or [given name]-chan because she wants them to be friends. I considered going with [family name]-chan as a combination of closeness, cuteness, and politeness, but that's apparently considered rude or sarcastic.

Kyoko is a middle class 15 year old girl. She's very distant, cold, and unfriendly. She calls her older step-sister [given name] and calls her classmates [family name]-san regardless of gender. I was thinking that she'd call her teammates [family name]-san too, as a way of keeping her distance.

Sugu is a lower class 14 year old girl who grew up in a tiny village. She's aggressive, short-tempered, competitive, and very impolite/casual. She goes to a school with a large delinquent population and calls most people by their first name without honorifics. The only exceptions are people she holds in high regard (who she might call [given name]-san or [family name]-san) and people she's mocking.

Nana is an upper-class 13 year old girl. She's timid, compassionate, quiet, and polite (maybe overly so). She calls most people [family name]-san, and even if she's told to use given names she'll call them [given name]-san.

Mikan is a working class 9 year old girl. She's cheerful, friendly, and both intelligent and mature for her age. It seems like it's common for kids to call other people (even adults) by their given names, so I was thinking that she'd do that too.

Ichika is a middle class 17 year old girl. She's a bit of an air-head, is immature, and tends to be overly friendly with others, she also has a love of all things 'cute'. She tends to call people [given name]-chin, even if it's the first time they've met. The only exceptions are 20+ year-olds, who she calls [given name]-san or [family name]-san.

Yuzuki is a working class 17 year old girl. She's arrogant, vain, dramatic, and a bit of a bully. She goes to an all girls' school and would call most of her classmates [given name]-san/-chan, or [family name]-san (for girls she doesn't know well), teenage boys and younger would be called [family name/given name]-kun. I was thinking that she could call people [family name]-chan as a way of being condescending.

Kei is a middle class girl 17 year old girl. She's kind, motherly, and mature, but also incredibly stubborn. Japanese isn't her first language, and she mostly sticks to using [family name]-san/-kun for people she's not super close to and [given name]-chan/-kun/no honorific for her close friends.

「Kyoko is a middle class 15 year old girl. She's very distant, cold, and unfriendly. She calls her older step-sister [given name]」

This would be pretty unusual. In Japan, younger siblings usually don't call their older siblings by name. It's generally oni-san/oni-chan/aniki when talking to an older brother, and one-san/one-chan (and in some rare cases aneki) when talking to an older sister.

A younger step-sister calling an older step-sister by her name is something that could theoretically happen, if the second marriage happened when the younger step-sister was no longer a little kid. Calling her by name instead of one-san would probably give the impression that the younger step-sister is adamant about not accepting her older step-sister as part of her family, though.

That said, calling the older step-sister just by her name (with no honorific) seems like it'd be unlikely in Japan. It's two steps below what would usually be polite (one-san → name + -san → name only), and it would go beyond simply being "cold and unfriendly" and come off like she's actively trying to start a fight with the older step-sister, which doesn't really fit with what someone with a "distant" personality would do.

「Mikan is a working class 9 year old girl. She's cheerful, friendly, and both intelligent and mature for her age. It seems like it's common for kids to call other people (even adults) by their given names, so I was thinking that she'd do that too.」

Kids calling adults by their given names, especially without any honorific, is pretty unusual in Japan. Generally, kids call male adults oni-san/oni-chan (for young adults), oji-san/oji-chan (for mature adults), or ojii-san/ojii-chan (for elderly adults). When talking to adult women, those become one-san/one-chan, oba-san/oba-chan, and obaa-san/obaa-chan.

Kids do often combine the adult's given name with these honorifics, though. For example, kids might call Taro "Taro-oji-san" or Hanako "Hanako-one-san."

「Yuzuki is a working class 17 year old girl. She's arrogant, vain, dramatic, and a bit of a bully. I was thinking that she could call people [family name]-chan as a way of being condescending.」

I'm not sure that calling someone by their family name plus -chan comes across as condescending. If anything, I think it'd sound flirtatious. In particular, a 17-year-old girl calling a guy by his family name plus -chan feels like something she'd be doing to try to show off how mature (since she's using family names) yet playful (since she's using the affectionate -chan) she is, or at least thinks she is. Speaking as a guy, if a girl I just met called me by my last name and -chan, my knee-jerk reaction would be that she's coming on to me, and in a fairly blunt, aggressive way.

● -kun

My take on this might not be applicable to all people/situations, but it seems like I hear -kun being used far less often in actual spoken Japanese over the past few years. I realize it still pops up all the time in anime and manga, but I think that's primarily because it's a useful dialogue shorthand to quickly show a characters' personality/relationships.

Personally, the main situation in which I hear -kun being used is when adults are talking about boys. Things like teachers calling male students -kun, or parents talking to their own kids about the kids' male classmates/friends and using -kun. "Tanaka-kun, please hand these papers out to the rest of the class." "How was preschool today? Did you have fun playing with Hanako-chan, Taro-kun, and all your other friends?"

-kun occupies a strange spot in the Japanese language because it's an ostensibly polite form of address, but it's exclusively used for talking to/about people who are either below you or on the same rung of whatever hierarchy you're going by (age, school year, position in the company, etc.). So it's simultaneously respectful and not respectful, which makes it tricky to use.

Because of that, it can sometimes come off feeling sort of like a backhanded compliment. During my first job in Japan, I once called a male coworker who I was on friendly terms with (we'd hung out a few times outside of work) "Saito-kun," which resulted in everyone else in the office laughing and instantly giving me the nickname "bu-cho" ("section manager") because calling him -kun made it sound like I was his boss.

Thank you for the detailed answer!

Kyoko was around 12-13 when her mother remarried, she really dislikes her step-sister for a few reasons. The biggest being that she associates the step-sister with no longer seeing her father, as Kyoko's mother cut off contact after meeting her second husband. She doesn't like admitting that they're related and actually feels a little embarrassed by her step-sister due to how childish and oblivious she is.

Since you said that [family name]-chan can sound flirtatious, what do you suggest I use instead to make Yuzuki sound condescending or mean?

「Kyoko was around 12-13 when her mother remarried, she really dislikes her step-sister for a few reasons. The biggest being that she associates the step-sister with no longer seeing her father, as Kyoko's mother cut off contact after meeting her second husband. She doesn't like admitting that they're related and actually feels a little embarrassed by her step-sister due to how childish and oblivious she is.」

Yeah, I figured that was the feeling you were aiming for. Having her call her older step-sister by just her name with no -san, though, would probably be seen in Japan as less a subtle dig, and instead as just plain rude. It's probably not the sort of thing that her mom and step-dad would shrug their shoulders about and let slide, since it would feel less like Kyoko is rejecting an intimate familial relationship, and more like she's actively trying to cause a problem.

Personally, for the emotion you're trying to convey, I think it'd be most natural for Kyoko to call the older sister by her name plus -san. Japanese people rarely call their siblings by their given names (in the 10 years I've known him, my Japanese brother-in-law has never called my Japanese wife anything other than "one-san" or some variant of it).

If, for example, a Japanese girl's sister is named Hanako, usually she'd be "one-san." If their relationship is a more casual, familiar one, she might be "Hanako ne-san" or "Hanako ne-chan." But calling her Hanako-san would have people thinking, "Wait, aren't you sisters? Why do you call her by her name?" That meshes with the emotion you're going for for Kyoko, but since -san is still an acceptably polite way of speaking, calling her step-sister by her name plus -san keeps the "I don't think of us with sisters" vibe without adding the feeling of "and because I don't think of us as sisters, I should be allowed to treat you worse than I other people."

「Since you said that [family name]-chan can sound flirtatious, what do you suggest I use instead to make Yuzuki sound condescending or mean?」

That might be something that can be better conveyed through other parts of her dialogue, as opposed to the honorifics she uses. There's no "mean" honorific, and while -chan isn't something you use for people higher up a hierarchy than you are, it also has an affectionate tone to it, so it doesn't really convey meanness. -kun has a similar problem, in that it's also not used to address people above you, but again, it's a polite term, and so not necessarily mean.

Personally, I'd probably write her as using family names with no honorific. The lack of an honorific shows a lack of respect, and avoiding given names implies "The reason I'm dropping the -san is NOT because we're close friends."