Since you mention that the coop is way to small for them to stay in all day, is it too small for them to comfortably roost?
Be sure you are using the 4 sq feet per bird for coop general range and that you have roosts that are higher rather than low to the ground. Most birds prefer to roost up high (natural instinct to prevent being eaten while you sleep by ground predators). Also are the roosts comfortable to grab hold of with their claws?
If you are confident it is not the coop set up, then it may be simply training them to go where you want them to go. I've had birds (usually game types) insistent to roost high on top of the coop (and trees). Some breeds simply have this ingrained more than others.
You may have to pick them off for awhile until they get the idea. The best method is to lock them in the coop until they get the idea to roost there, but if you can't do that, then retraining by placing them in the coop (with treats!) may do the trick.
Edited by blumenmadchen - 4/3/16 at 12:08pm
I am not positive its not the coop set up. It is small and the roosts are not very high. It is a prefab coop that we got talked into by a local chicken farmer (so I believed he knew what he was talking about). But it has been fine for almost a year. Did they just suddenly decide it doesn't work for them? They have always gone in on their own. Nothing has changed. They free range all day, and are only locked up at night. I really thought they were happy and doing well. I guess ill need to plan a new coop😞
If they have been fine for a year, then check for roost mites or other such parasites....something may be making the coop uncomfortable.