So regarding the Magic candidates,
@Mr.rodent has brought up a rather good point that the lack of lore knowledge makes it more difficult to choose between them and also to judge their worth. So I'm going to spell out a bit of why they're significant in this post here, and hopefully that will help.
Firstly Magic, or the Arcane Mysteries, as they are known to the educated (read:nobles), is real and openly acknowledged in this world. For all that though, they are not widely practiced. Why? Because Magical Knowledge is literally power, and the power in this setting is tightly hoarded and jealously guarded. I don't know if you've noticed on that map I made the other day, but the Alkadian Empire is not small.
So Sorcery is restricted to nobles generally, and even among that class, the knowledge is highly restricted. Magical items are rarer than gold.
One of the centers of magical knowledge in the Alkadian Empire, is the Alkaden Library, which is itself older than the empire. It's run by a secretive and exclusive family, and the fact that one of their librarians is running around out here on a "research project" is rather eye-catching.
The initial major benefit of Abren is that he can communicate easily with you, The initial major downside is that he's got side projects.
One of the other sources of magical knowledge is widely known as the Faith of Benevolence. They're a religious order that are the closest the Empire comes to having an official religion. They regularly commune with their god, Benevolence, and can perform visible miracles. Think clerics.
Unlike typical fantasy settings, the line between arcane and divine is rather blurry, and members of the faith who earn the right will often study
both. This is the major upside to Cerryl. He comes with a background of knowledge you won't find elsewhere. The major downside is that when it come to performing magic, he's limited to the divine half of things.
You should recognize though, that more than half of the actions available in any given round will be centered around theoretical research, for which he would be more than sufficient.
Zenthalas is an Elf. I was being too clever with the "showed up out of the woods one day thing". She's not crazy, but does have a vastly different, one might even say alien, mindset when it comes to magic. That's both the upside
and the downside. Also, no human who was the age she appears to be could perform magic as strong as she. So, yes, powerful on the performance end of things.
One of the reasons I gave all of the Sorcery options downsides is because magic is going to be something of a force multiplier in this quest. I haven't worked out the exact mechanics of how that will work yet, but hopefully you can see a little bit of how these candidates might be able to strengthen your position, whatever the case may be.