Aside from the position issues - which I covered in the last thread you started on this, and very much agree with Anebel's observations and suggestions - I can see that the shoulder and back have freed up quite a lot since the last group of photos. I'm glad to hear that you have taken some of my suggestions into account in your riding.
From this point, it is really going to be fixing your own riding now, that will loosen him up that step more, until he is truly free through the back, shoulder and hind leg. Right now, your position is making that impossible for him even if you ride him 'correctly' through the exercises, and he wants to loosen for you.
I know saddles are expensive, so is there a chance that you could try a few different saddles on him that you can borrow from friends, to see if they make a difference in your position and balance? This saddle is really doing you no favours.
Weights are brilliant as Anebel has already stated - I'd be doing a lot of pin loaded leg weights - squats are excellent for this (I did my first 80kg squat series in the gym the other day, very pleased!!).
But most of all, work on your core. Try and sign up at a gym and do core and abdominal building work, and if you can, attend some of the classes that gym's offer. I love to do the RPM and core building classes at least once a week.
You will really notice an improvement in your riding if your core is strong. I have not seen you engage your core in any of the photo's you've put up - which means you have to grip with your leg and rein to stay in the saddle.