I'd also say you're reaching, but if you really want to do it, I'd look to the three main races of the series (I think anyway): Yeerks, Andalites, Humans.
Humans=Soul (really more spirit, but
) While it was human bodies that made them so valuable is a war resource, this series (like 98% of fiction) highlights the human spirit. Humans are repeatedly called physically awkward and technologically backward and in stereotype don't fit body and mind, but it is again again pointed out that human resolve, fighting against all odds blah blah blah, and it's what's makes them incredible.
Yeerk=Mind. Again, it's their bodies that allow them to do it, but on their own, yeerk bodies are unimpressive. With the traditional association of mind and brain though, it's not hard to make. They are intricately linked to the minds of host, the body controlled by another's mind, and along with the species unarguable intelligence, it's a decent fit.
Andalite=Body. I know, want to give them mind, cuz they so dang smart. But in this series, the Andalites are more or less the long arm of the law, the physical force of order. At the same time they are the ones getting beat, constrain by their physical (military) limitations. Andalites at least the organized military at large are also often the case for being swayed-they are much more corruptible than strong mind and resolute spirit, where a mind is willing, but the flesh is weak, so to speak. Finally I guess, their own bodies are some of the most formidable in the series.
It wouldn't be that any of these groups is without the other features of course, but there is one they represent more strongly than the others.
If you really want to stretch, you can do it in the Animorphs group itself and show duality in some of those features
Soul- Rachel & Cassie; passion and compassion, respectively
Mind- Ax and Marco; knowledge & strategy
Body-Tobias & Jake; Tobias as your sensory input, information acquisition, physical transit and in some respects flag (what yeerk on earth doesn't know a red-tailed hawk?) and Jake, the leader, the symbolic head that provides the other elements cohesion. (okay this one's a bit bigger stretch, and you arguably could shuffle Tobias, Ax and Jake around in mind/body)
They are more trinity than trichotomy, (if I know what trinity means
) but a statement of necessary interaction between parts to form a functioning whole: for the Animorphs, a team, for the story, an integrated plot.
Yeah, that makes sense