You have problems with your elbows because you have "puppy dog hands" fix your hands and your elbows and shoulders will follow.
It looks like you're shoving your heels down too far. The way to correct it would be to lengthen your stirrups one or even two holes and change the postion of your foot by pushing into the stirrup a little more with the ball of your foot. Be careful not to change your leg, as it is in those photographs, it is positioned correctly in the saddle and at a proper angle.
Thank you. I'll lengthen them a hole next time.
Could the problem with my jumping ahead be that I'm jumping up and forward (out of the saddle) and causing my leg to slip back? I was studying other pictures of riders and it looks like they're jumping up and back (out of the saddle) and they're getting legs underneath themselves, flat backs and non-chicken wing arms.
Your sitting pic looks a bit short, but then I noticed that your action shots you were more low with your heel/anckle and looked much better. Try it one hitch longer for a few days and see how it feels. Maybe just sit a trot for a bit and don't post. See how low you can post and still get the job done. If you are posting to high, that would mean the stirrups are too short.
When you start doing the large jumps, things change. That's my 2 cents worth. Still very nice.
It would be a great help if you had some jumping pics. I have an exersize that may nelp you understand what is happening when you jump:
Start by standing straight with your feet close together shoulders back.
Bend both legs so that you are standing with your legs bent as you would while riding a horse.
Lift your left leg approx 1" off the floor.
Bend forward at the waist while maintaining the position of your right leg.
You will notice that your left leg will naturally stretch back to aid in maintaining balance.
Now repeat the same exersize but this time, push your bum back, your lower back down and push your shoulders back and together.
You should feel a major change in balance compared to #1.
Lastly, do this (minus the leg lifting bit) on the flat, and then once you feel comfortable, while jumping.