"Hello, mate. I'd just like to pose a question to you concerning the Battle Chatelaines. Actually, a few questions, really. 1) How does Serena get along with them in this universe? 2) Have any of them got any significant others that we don't know about? I mean, Professor Laventon is married to Cyllene, so there is that. 3) Why are they so inexplicably Irish when they live in France? What's that all about?"
These questions will be answered out of order for the sake of this response's narrative structure.
🤎 In the original Japanese dialogue of XY and Omega Ruby and Alpha Sapphire, the Battle Chatelaines speak in the Hakata dialect which is spoken in the Fukuoka Prefecture located in Kyushu, which the Hoenn region is inspired by. In the former game, this seems to be meant to foreshadow they were born there and would also be making an appearance in the latter.
Giving the Battle Chatelaines Irish accents in the English versions certainly was... a choice. I can only surmise something occurred behind the scenes of the localization process, something involving the translators of XY remaining unaware of their connection to the Hoenn region until Omega Ruby and Alpha Sapphire, and in XY the intention was to imply the four are from the Pokémon world's equivalent of Ireland despite no region inspired by Ireland existing then (or now) - similarly to how Fantina frequently implements French phrases into her speech, which presents the possibility of Fantina being Kalosian two generations prior to the introduction of Kalos.
But in Sisterhood's universe, Morgan, Dayna, Evelyn, and Nita retain their accents and aren't Hoennian. Rather, they're multiracial; one of their parents is from the Pokémon world's equivalent of Ireland and the other is Kalosian and Galarian. The Battle Maison in Hoenn also functions as a summer holiday home for the family, because they're relatively wealthy and are considered members of the aristocracy in both Kalos and Galar.
🤎 Serena is the daughter of Grace the Rhyhorn rider and a greatly successful Silph Co. businessman, so she's a member of high society herself. It's quite probable she's met the Battle Chatelaines previously (as well as Steven, Caitlin, Jacinthe, and perhaps Nemona), since her family did live in the Galar region for a time before eventually moving to Aspertia City in Unova and then Vaniville Town.
Out of the four, I believe Serena would be most comfortable in the company of Morgan, followed by Evelyn. That isn't to say she dislikes Dana and Nita (there are few people Serena does), but the second eldest and youngest sister secretly harbor some amount of jealousy towards her due to the attention she attracts at parties, then later her strength as a Pokémon Trainer. The two have a tendency to take these sentiments with them to the tea table, so Serena feels as though her presence isn't as welcomed by Dana and Nita compared to the eldest and second youngest sister.
🤎 This section features Avery, or rather a certain member of his family! Sisterhood actually has a few original characters: Calem's older sister, Team Neo Rocket's trio of executives and leader, and Avery's older brother and younger sister.
Avery's older brother(24), Montano (his name originates from the binomial name for the herb winter savory: Satureja montana), is tall, thin, pale, has platinum blonde hair as long as Avery's, as well as icy blue eyes. And although he's physically frail, to the extent he uses a wheelchair and is narcoleptic, Montano's psychic abilities are irrefutably among the most powerful in his family's long history.
How does this pertain to the Battle Chatelaines? Avery's family is also aristocratic, they're outright nobility; Montano is as a matter-of-fact Lord Montano to most of the Galarian populace. He's to be the next head of the family someday, so his parents have selected another powerful Psychic-type Trainer to be his fiancée - Lady Caitlin of the Unova League's Elite Four.
The issue with that is, aside from them making such a monumental decision without his consent, Montano meets and falls in love with Evelyn during the evening party announcing the engagement. Both are seeking solitude in his estate's garden, but they find one another instead. Avery is regarded as the black Wooloo of the family, but unlike his siblings and parents, Montano is mild-mannered, softspoken and gentle. His personality melds with Evelyn's perfectly. He finds her shyness lovely, such a contrast to the other ladies he normally meets at these sorts of gatherings, and his calm aura soothes her nerves in a way no one else has quite been capable of... when he isn't indulging in his hidden mischievous side, that is.
Evelyn leaves the party feeling terrible for developing an infatuation with a taken man, and unknowingly in possession of Montano's heart. This was the best night of his young life, and it was spent not with his betrothed, but in the company of a woman he knows well his parents would never approve of, because Evelyn possesses no psychic power. No one around him can deduce the reason why he's become so melancholy the days following the party when Montano has such a beauty for a bride.
Avery is a disgrace in the eyes of their parents; he was only chosen as the heir of the Psychic-type Gym due to the symptoms of Montano's narcolepsy suddenly worsening and their younger sister(16), Hortensia (her name originates from the binomial name for the herb summer savory: Satureja hortensis), displaying such a terrifying temper whenever she loses a battle, it makes Whitney's and Clair's responses seem entirely reasonable by comparison.
But Montano can't stop himself from envying his younger brother's circumstances now. He may be a one trick Ponyta, but him lacking great psychic power means Avery has been granted the choice of who he is permitted to love.
I could also envision Morgan and Nita paired with Ingo and Emmet respectively: the courteous and mature elder siblings and the proud and somewhat mischievous younger ones.
(My adoration of shoujo manga tropes is showing in this section. I find this sort of drama highly entertaining as long as it ends happily~)
