i have found that stock birds keep healthier, last longer if flying out, but if you need to keep them in , the worst thing usually is fat,, with no excercise they will get fat very easy, when breeding and moulting they will need proteins , but at any other times would feed avery light diet, with less proteins,
a simple thing to stretch their wings, at least a little is to cut a round piece of ply, the same size as the base of your drinker, place on a pole in the ground of your aviary, as high as your aviary will allow, the then the drinker on this, the birds will have to fly up to the drinker, grip on to the side of the drinker, still flapping their wings while they drink, every time they drink they will at least stretch there wings each day, a few times , allways make sure they have fresh grit/minerals /pickstones, again place these , where they will have to stretch their wings to get at them, plenty baths will also help keep them in better condition as with some greens occasionally