Don't let it be a mental anguish.... We humans tend to believe that a colony or even a pair bonded to each other will remain so for life, that isn't true. Things change, dynamics change, gliders change, environments change etc...
In the wild when colony dynamics change the gliders are free to leave or are forced to leave the colony, in captivity they do not have that luxury. In captivity all they can do is give the human signs whether that is bickering, fighting, wounds, etc.... the human has to be aware enough to see these signs and make the changes needed to restore harmony since the gliders are imprisoned in a cage and can not do it themselves. It really isn't that uncommon to have to remove a glider from a colony and repair them to another.
The other thing to the " who am I to decide" is... you ( or some other human ) already decided they were going to be a family so you also have to be the one to decide when it's time to readjust that same dynamic.
As for will Axle taking issue with one of the others after Chester is removed... I won't assume, but in my experience I'd say no I don't think that is likely.
I've had experience with 2 girls not getting along once they were separated the others in the colony got a long fine.
I've also had one with a neck wound that once repaired had no more issues.
Underlying medical issues could be anything, gliders hide their symptoms very well because if one is ill the others in the colony can and do either run them out of the colony or try to kill them. By the time you actually see symptoms it can often already be to late.