In the first picture, your stirrup has slipped back on your foot and your heel is level with your toes, thus your weight isn't in your heels.
In the second picture, it looks to me like your butt stayed in the saddle. Were you left behind or something? (Just curious).
In the third picture, again your stirrup has slipped back on your foot and your heel is level with your toes. It seems like you are riding pretty drastically for a jump of this height.
In the forth picture, I can see almost the entire saddle behind your butt and it seems that you are on the horse's neck.
In the fifth picture, it looks to me like you sat too early. Don't sit down until all the horse's legs are on the ground.
In the sixth, it's kind of hard to critique this angle so take what I say with a grain of salt. It kind of looks like your leg slipped back and your thigh is lifted off of the horse.
In the seventh, you are toeing out very drastically, so that your foot and probably your thigh is at an odd angle compared with the horse's body. it seems that may have been helped by your stirrup, again, slipping back.
The next two pictures have the same general mistakes so I won't comment.
The last picture, you can see that your leg has really slipped back and your heels are up.
My advice for you would be to really concentrate on strengthening your base. I understand you had long stirrups, but it looks like your legs aren't as strong as they should be, meaning that you can't support yourself properly over the jumps- which may be the reason why you over-compensate with your upper body and look like you're trying so hard (if that makes sense). Lots of no stirrup work with some bareback tossed in. Your release looks kind of inconsistent to me- sometimes it seems not enough, too much, or just right.
Hope I helped and made sense!