For starters, you should shorten your stirrups a BIG two holes! At the length they are now, they are offering you no base from which to follow your horses motion over fences. Once they are shorter, you will be able to sink weight into your heels and anchor your leg at the girth. They have slid back on the first pic because you have no base.
You seems to be a gutsy athletic rider, but you tend to want to jump for your horse. Relax. Let your horse close your hip angle.
Your upper body is extremely ahead of your horse, and this also stems from your too long stirrup. You are throwing your body ahed of the horse to compensate for the lack of security in your leg. If you didn't throw yourself forward, you'd probably be left behind the motion.
In the first pic (as you stated) your hands are planted on the horses neck, right at his withers. The other picture is blurry, but your release looks to be the same in the second jumping pic. Remember, the point of a release is to give your horse freedom to use his neck and support for the rider. You are defintely pressing your hands in his neck-which is good, you don't want them above it- just concentrate on giving your horse more rein. Slide your hands farther up his neck in a long release. This way your hands willl be under your chest/head and offering you more support. You don't want your chest to be in front of your hands. I couldn't really see the jumping pics too well, so if I am wrong in this, sorry!
Keep up the good work!