But they were only tested for a few things I would imagine, they could have picked up something else.
I'd hesitate to worm without doing a fecal first.....but pay attention to withdrawals if you decide to go ahead.
The older ones, and maybe even the youngers, may be getting ready to molt.
Any chance they had a predator scare?
Are they free range or in a run?
Any changes in the run or yard?
Any changes in feed?
Are they eating drinking pooping normally?
Reasonably mobile and active?
Bug check:
Best done well after dark with a strong flashlight/headlight, easier to 'catch' bird and also to check for the mites that live in structure and only come out at night to feed off roosting birds.
Wipe a white paper towel along the underside of roost to look for red smears(smashed well fed mites).
Part the feathers right down to the skin around vent, head/neck and under wings.
Google images of lice/mites and their eggs before the inspection so you'll know what you're looking for.