So this is one of those cases where the themes and tones just don't really align, despite some surface similarity (honestly, YW is just very hard to cross with a lot of other properties because of how different its values and mechanics are from the mainstream). Just to pick one, a major element in Animorphs is the lack of any sort of external support structure, while the presence of an external support structure is a critical aspect of Young Wizards. Also, from a strictly mechanical standpoint, the power levels don't work: Wizardry invalidates the Yeerks on every level.
With crossovers out of the picture, what about dropping the Animorphs into the world of YW?
I don't think Jake is a Wizard. He doesn't have the drive or the curiosity at that age outside of some major external factor providing motivation for him, and Wizardry doesn't really work that way: the Call may know where you live, but if you aren't going to jump at it, it's probably going to leave you alone. If Jake finds out he's friends with a Wizard, I think he probably supports them how he can, but otherwise just lives his life, Harry Callahan-style. If he does somehow become a Wizard, I could see him maybe focusing on integrating Wizards in collective workings, maybe eventually becoming an Advisory to coordinate his local team.
Unfortunately, no matter how much I love him, I'm not sure canon!Marco would ever be offered Wizardry either, despite the fact that mechanically he'd probably be very good at it. "Wizardry does not live in the unwilling heart," and Marco was always ready to cut out; it also requires some level of compassion on a large scale, and if you're not in Marco's close circle, he isn't going to piss on you if you're on fire. Assuming he's exposed to Wizardry from another source, I see him going the route of Carmela: studying technical details of the Speech, forming business/technological partnerships with aliens, and supporting his Wizard friends where he can. Alternately, if Eva never "died" and Peter never collapsed, I could see Marco growing up with more empathy and openness and becoming a Wizard; in that case I see him specializing in technology integration and/or spell design.
Rachel I could see being a Wizard, possibly following a route similar to Dairine: she finds out her best friend's a Wizard and thinks that sounds so awesome she needs to get in on it too. I think she can still tend towards aggression, but the different mechanics and added support structure help keep her from going as far down that road as she does in canon. She's also naturally inclined towards communication and interpersonal skills, both of which have solid applications in Wizardry. She does have personal beef with the Lone Power, but her interactions with Crayak suggest her risk of overshadowing is not as high as it might otherwise seem.
Ax is a Wizard from a family of Wizards and he's not fully comfortable with that. It takes him a while to come into his own while dealing with cultural pressures and comparisons to his brother (who may or may not have died On Errantry). Eventually he finds his place, maybe specializing in time-based Wizardry, possibly after an exchange trip with an odd backwater planet it's natives call "Earth."
Cassie and Tobias are absolutely Wizards. As soon as they get offered the chance they jump at it. They're basically platonic Nita and Kit. Cassie's connection with the animal world is top tier and she also has an uncanny touch with transformative and chronal workings, while Tobias has a knack for clairvoyance and interspecies/interplanetary relations.
As a bonus, James is also absolutely a Wizard. He uses his Wizardry to accommodate his own paralysis and to help the kids in his ward where possible. He focuses on medical Wizardry and also acts as an advocate for disabled kids.