I see you asking about motif instruments, and i raise you: what would be the general vibe of your OCs' themes? Like say an OC, any OC, is introduced, what sets the tone?
(Ofc could pick any oc, or do a lot of em, anything you'd like to answer)
Saft
As I mentioned before Saft's motif/instrument if likely a fife or you know any sort of light fun flute instrument. I'm not good at explaining this stuff but like I can imagine perhaps... Okay so you know the original Disney Peter Pan soundtrack? He sort of has the same instrument to represent him too! With three introductory notes that almost sound like him crowing. Imagine something simliar for Saft and I think that's her sort of tone. Her theme needs to be very free spirited and fun, but also something that could be flipped to sound sad during her more emotional/moody moments.
If I want to get into Saft's headspace if I'm making art I often throw on the Tangled or Lord of the Rings soundtracks.
Arona
Arona is a elegant girly but also creepy AF Soooo what if her musical notifs were a mixture of Saft and Ravus' but when it comes to Ravus themes they're played in major and when it comes to Saft's motifs they were played in minor key? Like you have this whole vibe she's supposed to be sort of related to these other two characters but you can't quite work out why.
Instrument wise? Oh we're definitely getting a harpsichord and a violin melody? You know that part in Roxanne from Moulin Rouge where you just hear the violin and the strings go like REALLLY Slick and the melody starts to get more intense and scary? Horror movie vibes? We'd get a lot of that when it comes to Arona's more intense scenes/menty b's
Geel
Loud brass instruments probably, Anything that makes him sound extremely up his own ass. We're gonna get some cymbal crashes here and there too. Loud and obnoxious just like he is. I don't really have any good examples that come to mind.
Geel is sensory overload to the max. With any luck if Meuric's on the scene his accompanying themes will mellow things out.