There is something I've been meaning to ask you: do you have a headcanon for what the Kelbrid and the Anati might look and be like?
Something we didn't get a ton of in Animorphs that I'd love to see more: dramatic size differences or dramatic difference in styles of communication. So since the Kelbrid are described as "mysterious," I like to imagine they're sort of like the veleek — both much larger and much smaller than a human, maybe not exactly like the veleek is but in a way that renders communication between the species basically impossible:
Anati have a few more constraints on them, seeing as you can definitely get a yeerk inside of them so they're at minimum a Class 3 species (central brain + some kind of orifice + basic survivability in an andalite-designed environment). We also know the yeerks ultimately lose that segment of the war, so I like the idea that they get underestimated. Maybe they're only just bigger than yeerks themselves but with massive brain-to-body proportions so they're basically all skull with tiny limbs that also excel at predation enough that they can fight off the yeerks: