I think it was just 23 (though I don't remember it being that exact number it sounds bout right) they kept the number small(ish) and must have taken some losses over the course of things. I can believe that there were only 23 aux-animorphs.
Only 23 children sent on a suicide mission, made to watch as one by one or in small groups their friends were vaporized by an enemy they couldn't fight back against, who had to wait their turn hoping that by some miracle they'd survive. Can you imagine being that helpless, seeing everyone around you dying and knowing you can't do a thing about it? To have an enemy you can't hope to hurt make sport of you, slowly targeting one animal after another, drawing it out for their enjoyment while you, a child, have to keep marching, keep on going, you can't run, you can't escape and all around you your friends and comrades die, no way to avenge them, no way to save them.
23, 100 or 1000 as far as I'm concerened that's suffering, the lower the number only shows how much longer Visser 1 dragged the game on.
They're barely even mentioned when its over.
It was a sad scene but also a great one because of the bravery shown by the auxiluries and because it solidifies Visser as a villain, not some cooky old man who cries "you meddling kids!" every so often. A truly epic moment in Animorphs.