I'm picturing like taxxons and hork-bajir and yeerks working together in the background to overthrow the empire. (On Earth at least?)
No one really keeps track of the taxxons, especially not the old ones and definitely not during lunch even if they don't have their yeerk in. They're real voluntaries, unlike most of the humans that don't go to the cages. They're free to eat wherever they like provided it doesn't compromise the invasion. Who cares if a few like to hunt deer deep in the woods as long as they come back.
The highest host casualties are the taxxons. Even their masters can't keep them from devouring each other at the drop of a hat or leg. Their hunger is too strong to fight. Which is why no one bats a stolen eye at what is clearly the aftermath of a frenzy, blood on the floor and legs still being crunched in red taxxon mouthes. Who'd bother to investigate closer and see the faint lopsided prints half covered by disturbed dirt? Or what might be a collapsed escape tunnel mostly obscured by a fed taxxon cleaning off a comrade's blood from their lips.
The hork-bajir scream "Free of Dead!" at the top of their lungs and fight fiercely every minute that a yeerk is in their heads. They mean it too. A single lapse in control can end in one of the stupid things stabbing themselves with a blade. Holding a hork-bajir is stressful, many move on to something easier.
But.
There are those few lucky bastards who get assigned to a hork that turns out to be voluntary. They never reveal the secret to it or how they get the things so damn loyal either. At least one got reassigned to a more useful yeerk and drowned itself on pool sludge before the new yeerk could even climb in.
Of course, even if their yeerks might be up to something, the hork-bajir themselves are too simple to suspect. They can't even figure out how to play Go Fish properly.
The voluntary hork-bajir on their part have no intention of clearing up that misnomer. They were in fact very good at Go Fish and even better at poker. So good in fact, that the disgust and pity from their caged comrades are genuine. And while the free colony that comes later disagrees with their methods, the notes they hide in the curves and crevices of trees are worth their weight in stoola honey.
Way before the adventures of Afran in the woods alone with the andalite bandits, there were yeerks who did not agree with the whole empire thing. Since the day the rebellion against the andalites started they lurked in the pools. And when the leadership decided that disagreement was something to punish with death they whispered amongst themselves and very very carefully found like minds in the younger generations.
The Yeerk Peace Movement is only one of many dissenting groups. Derided by the more militant ones for their unwillingness to take up palps against the evils of their society. The hork-bajir don't pretend not to hate them all regardless of their stance on things. But they're willing to work together for the day they'll never have to interact again.
And while no one trusts the taxxons as far as they can throw them, the worms are willing to dig unregulated pools for them. Set up kadrona rays made from stolen parts and generators hidden deep in new hive tunnels far from the main yeerk pool.
The andalite bandits are a godsend.
Hosts slip away at every raid, sneaking in the opposite direction as all the chaos. Computer records are mysteriously tampered with in the wake of the destruction of the ground-based kadrona. Yeerks with no witnesses to their demise are marked deceased. And when the morphing technology becomes available all hell breaks loose.