Mortimer is probably the default spelling, Mawr-ti-mer according to Behind the Name. I spell it with a slightly stronger t because of how portuguese phoenetics work though, but that's a personal thing.
Veriesin is Ver-ay-e-seen. She's supposed to be a combination of Vera and Taliesin but I actually didn't know how the stressed vowel was spelled for the longest time(Taly-es-sin), it still works but it's not how I spell it at all since her nickname is just Veri.
All the Amberhobs are their nouns separated if applicable, so Spinel-thorn, just Fangs, etc. Audrey is also the same spelling as the normal name.
Elise is a variation of Eliza that's been part of my stories for some time so I don't remember exactly why it was changed, spelled El-iss. A very VERY silent E at the end.
That's just the main characters though. Everyone else generally is spelled the way you read them (except maybe Quasannon(Quas-annon like Rhiannon) with no big changes - on the comic. In the larger universe there's a lot of weird ones that'd take too long to talk about.