There could be several things going on that could cause that.
first thing to check for is external parasites, injury. call and ask a vet if he will do a fecal float test most will this will tell you if they have internal parasites.
What does their poo look like, if it has a pink or red tinge they could have gotten coccidosis, that you would treat with corid.
If fecal comes back with worms then you treat that with a couple different ones depending on the type of worm, worms can cause a lot of different symptoms if they have a worm over load and your flock hasn't been de wormed lately.
They could have gotten something in their ear or an ear infection thats causing Vertigo.
And lastly what are they being fed, they should be on either chick starter or all flock as roosters don't need the calcium a layer does and it can cause liver problems. Treats should not be more than 10% of their feed.