Considering your history, you're doing an amazing job, particularly since you're working without help. Of the four photos, the 1st and 4th show the best overall position.
You have two form faults/tendencies you need to work on -
First, A tendency to grip with the back, rather than the flat of your calf, which in turn forces your toe out, which in turn creates some pivoting on the knee.
Second, A tendency to overjump/overclose your hip angle which leaves you too close to the horse's neck.
Photo by photo -
Very slight toe out, lower leg slightly behind perpendicular. Weight in your heel, but stirrup a little too far back on your foot. Should be on the ball angled across your foot so the outside branch of the stirrup iron touchs your little toe. Crotch over the middle of the saddle, buttocks out of the saddle the correct amount of the size of the size. Too closed of a hip angle for the size of the fence, laying on the neck. Long release accentuates the laying on the neck and is causing you elbow to pop out. If I could only change one element of this photo, it would be to move your hand and arm 6" forward. That would fix the elbow and part of the laying on the neck.
Second photo - more pronounced grip in back of calf, more rotation of the toe, and lower leg further behind you. Stirrup still too far back on foot. However, you're still over the center of the horse and out of the saddle the correct amount. Big roach in your back, and too close to the neck. Medium length released executed well with elbow in.
Third photo - Adding heel up to your lower leg woes. Base of support still good, eye up and looing ahead, but still too close to the horse's neck. Good medium long release.
Fourth photo - too dark to see lower leg, but I suspect it has slipped back. Here, the one thing I would change would be to pick your shoulder and upper body up off the horse's neck, it would change the look of the whole photo.
I like your horse very much; and he looks to have scope and talent to spare, however, he doesn't look like he has a lot of respect for those skinny PVC rails - he's a little casual about his front end. It's not lack of ability, certainly. I'd like to see him sharpen his form a little.
Good luck, and please post back with some new photos after a while.