I'm not that familiar with US or UK voice actor,s but I do have a few in mind.
I mostly went with characters of similar personalities to try and pin down a good voice
Vernon - Cristina Danielle Valenzuela
I originally thought her a bit to energetic, but I saw her dub of Xinqiu from Genshin impact and found she has can hit close to the notes he hits with his calm speech, not sure if she can pull the anxiety though.
Azreth - Ian Sinclair
This one was picked even before you asked, I often conjure in my head a the voice of Zaveid from tales of zestiria/berseria to match Azreth's tone and manner of speech. Not sure how he would feel about Azreth naughtier and more jokster side, but the voice is perfect.
Grey - Liam O'Brien
This one is tough as Grey has a particular way of speaking and heavy accent and tongue problem, so finding someone with a similar voice is troublesome if not downright impossible. I did inspire him a bit on khajit from elder scrolls, but that is too much a of long shot... So yeah, It is tough for zhe lynx man...
Also... No... He doesn''t talk about himself in the third person.
EDIT: So my husband actually sugested Liam O'Brien due to his work as nightcrawler, personally I think he's got the range to pull just about anything so yeah, I'd think he can pull off Grey. Would be interesting to see how he approaches it though.
Drake - Jason Liebrecht
Particularly because of his work on Dabi from 'Boku no hero' I think he would be a great fit for the edgy (pun intended) obsidian dragon who wants nothing more than to torment his brother.
Lisa - Allegra Clark
A strong female voice for a strong woman who wants nothing more than to do her job well. I picked her for her voice on Beidou in Genshin impact BTW.
Yggreth - Griffin Burns
I heard his voice perfect when I heard the english dub of Tartaglia in genhsin impact, you can practically hear the cocky smile everytime he speaks.
Hemlock - Edward Bosco
The guy got an amazing range, but the voice that comes the closest is one of his less known works... He dubbed Baron Samedi in smite, and he was a big inspiration for me in the creation of Hemlock, so it makes sense to cast him here.