I'm not really sure what you concern is here. What are you going to do with the flock if you don't take them? Leave them where they are? Do the new owners want them? Do they know how to take care of chickens? Or are you going to kill the chickens before you move? Are you planning to give them to someone else?
Frankly, if all that was wrong with the birds was coccidiosis, there is no reason not to take them, unless you just don't want them anymore. Coccidia are everywhere, and you do risk them being exposed to a new strain in the new house, but you can treat them again if needed. If you are worried that they will bring some unknown disease to the new house, they would take that (if they had it) anywhere they go, so to avoid spreading unknown disease, you would need to cull them, really. It wouldn't be fair to any new owner to pass that on. If the remaining birds are healthy, why not take them? If they are not healthy, best to cull them.