I personally would want the two who have never had the bloody stools off of the Corid and on to vitamins. I would direct dose them with nutri-drench. I would direct dose the other two with the corid.
IMHO all of your chicks have been exposed to coccidiosis, and you have treated even your healthy chicks for it, so it should be ok to put the two you suspect having wry neck in with the healthy chicks. But if you want an easy 3rd space for them, use a cardboard box. You have room for that and you could put the heat lamp between the two brooding spaces.
Hoping the best for these little ones.