You could also go with the silly theory that since they are identical-looking reinarnations of Silver Milennium people, their geneology is basically Lunarian, while Mamoru, Helios, Beryl, and the Shitennou are probably from a fallen kingdom in either Antarctica or Greece. And then Chibi-Usa is a combination of those two things.
As far as race in anime, I think there are some cases of non-charicaturized people with dark skin who are supposed to be from foreign countries, though what counts as architecture may vary. For example, Kaolla Suu in Love Hina has dark skin, blonde hair (or sometimes it looks kinda white or greenish, depends on the colorist), a Bindi/Pottu type dot on her forehead, but she's from some madeup kingdom called MolMol that's probably located in a slightly different "magical world" (or so I retroactively infer from the author's next manga in the shared setting). She doesn't have any exaggerated physical traits compared to any of the other characters (though all the characters in Akamatsu's manga are pretty sexualized, but that's a whole other topic and that also applies to Sailor Moon anyways). She does do weird things, but basically everyone in that series acts sort of crazy, and if there was a specific racial subtext I didn't pick up on it. But there's probably much better examples out there, that's just one I know about.
I forget if I already mentioned this, but, I do kind of halfway like the idea of a Sailor Senshi functioning in a wheelchair. Given the way attacks work, I could see them pulling it off, but navigating would be a frequent problem (especially doing so quickly). But since they have futuristic moon technology and stuff like the Mercury Goggle, maybe it could be a ridiculous motorized wheelchair like in the movie Steel or Alien Resurrection?? I doubt they'd go that direction in the Toonmakers/Saban version though, or even think it out very well in terms of plot impact; it probably would've just been awkward.
...unless the Wheelchair was supposed to turn into this.