I agree they need some groceries. Alfalfa should be third cutting or later for most horses. Watch the protien levels . If they grow to quick they get the joint diseases. It looks as if the first horse is standing on a hill, if not, then he is very butt high. At this point he looks as if he would be good for flat work.
Regular exercise, even if they are just in a pasture is great for young horses as they learn where and how to place thier feet without the stress of "training"
Hope they turn out like you wish