Ah, lazy horses are so wonderful, are they not? ;) haha. My horse does the same thing.
The shoulder issue: I would carry a little crop/bat in my hand. Try to support them by mentally picking up their shoulder. Look forward, put the inside leg on him at the corner and lift the inside rein. The best way is to do smaller circles everywhere. Sometimes I'll hold it until my horse lifts his shoulder and beds his ribcage around the circle, then I quit. If he blows his shoulder out on you when on the rail and turning, make him go do circles in that direction, keep with it until he gives and moves correctly. If he blows it out past your leg, pop him on the shoulder he's blowing with the crop. Always use the crop last, though.
Forehand issue: I'm not sure how you're riding, you might be fine and he might just be lazy. Which means you will have to work yourself that much more. It also might be hard for him to collect himself due to conformation. Usually a forehand horse is due to a heavy handed rider, however. get lighter and more supple in your cues, using your body (leaning even before putting the leg on him for a turn, then rein as a last resort). Also, Imagine lifting his belly up. You will have to hold him at a walk/trot, wrap your legs around him, and just think "lift". It sounds really strange and I admit it's hard to describe, but your body usually figures out what the cue is. When your horse responds, you will feel his back lift up into you. He might get it confused with "faster" though, so it will take some trial and error on that part. To get his head to drop and get his hind end under him, hold him steady at a walk/trot, and use your seat and legs to "push" him forward into the bridle. It takes a lot of imagination to get these cues right, which is why I think so many people have a problem with it. Open up your hips (kind of stick your knees off of the horse) and tensen your own bum and squeeze him forward, but don't let your hands go all willy-nilly so he can get all sprawled out again. You should feel him get under himself and see his neck pop up, he should bend at the pole and have his nose tipped in slightly.
Practice makes perfect, and it actually takes a LOT of muscle for these things, so don't expect perfect results right away :)
Mother to three amazing rescue babies<3 ~Pele ~ 4/5 year old palomino appy filly.
~Papillonn ~ 20 year old arab gelding. ~Ruby ~ 3/4 year old flaxen chestnut BSP filly.