I think Mashima vastly underestimates the influence people can have if they’ve known each other a long time, especially when you meet those people during your developmental years. Which is why I’m of the opinion that Lucy, as the only one to have never been part of a guild before, would behave in an incredibly separate way to them.
Most of the kids who came to the guild were under ten/severly under developed because of trauma, which in my personal opinion is the time when you pick up the most habits from the people around you.
Ex:
Natsu definitely calls babies, hatchlings and toddlers, fledglings because that’s what infant and adolescent dragons are and he’s never been around human babies/children. Now I’d imagine Erza picks up this habit because she has also not been around people that addressed children in that way. Obviously people try to correct them but eventually all of fairy young do it, at least when talking to Natsu and Erza.
Gray had a thick accent when he was younger and when he was frustrated or forgetting a word he would swear in his native language. Cana as his only friend would pick up on this and not only learn the word in his language but she would also tell him the word in Fiorien before he could get frustrated, and picks up a new swear word to use. This extends to fairy young as a whole, they trade language tips, swear words and eventually the guild becomes a melting pot of different languages.
Levy realized that a lot of fairy young had no idea how to read, which is why they weren’t interested in books at all, so she would get into the habit of reading out loud. Of course loud enough for everyone to hear and now when she’s in large groups of her friends she’ll start reading out loud off reflex.
Elfman learned how to sew/tailor his own clothes because Magnolia doesn’t sell clothes his style in his size for someone his age, he also sewed his own name into the tags because he wanted to be able to call someone out when they borrowed his clothes. Once Gray starts really losing money from not being able to prove his clothes are his Elfman teaches him a bit about tailoring and Gray sews his name into the tags to the present. (Got this idea from a fanfic but I can’t remember the name of it.)
Gray only had a passable reading and writing ability when he first joined the guild so when Cana taught him how to read and write, he scrawls his capital letters the same way she does. When he teaches Erza to write she holds her pen the same way he does. When Erza teaches Natsu to write his letters lean slightly in a cursive like way in the same way hers do.
