If it is worms you need a wormer medicine. ACV won't get rid of worms. I dare say you probably need to worm them if you have never, without performing a fecal test. You could also start them on a round of Corid at the same time too.
If they free range, then they should probably have free choice oyster shells for calcium. Layer feed has the right amount of calcium for that amount of layer feed and not for free ranging food and table scraps.