Sorry if I say something that's already been mentioned (I havn't read previous comments
In some of the pictures your leg looks too far backwards, is that because you were pushing him on? Or was it just in that position? To secure the lower leg I would first suggest lengthening your stirrups a little because at the moment you are perching on your horse rather than sitting deep into your saddle. Once you have a longer stirrup it will be easier for the weight to flow through the leg and into the heel. You shouldn't really have to force the heel down, it should happen naturally. I'm not 100% but the way that your lower leg seems to move a lot suggests that you are pivoting on your knee, tensing it and fixing it against the saddle. I do this sometimes so I know how hard it is to break! You really need to get your knee off the saddle, totally relax it and allow the weight to flow through it. That way you will be able to wrap the lower leg around your horses, securing your lower leg and keeping the heel down.
To get the toes in, grab the back of your thigh and pull it out and away from the saddle. This sets the whole leg in the right place and therefore the toe will not be forwards. Also, a good thing to do is lift your legs to the top of the saddle and as you let them back down again, really pull them away from the horse and aim for the hocks of the horse. That will allign the leg properly too.
In some of the pictures you look like you are putting too much weight on your pubic bone. The weight should be distributed over 3 points, the seatbones and the pubic bone. Really think about rolling backwards so you have equal weight on all 3, I have to really focus on it to get it right. This will help stop the shoulders rolling forwards, and therefore keep you more back and upright.
Of course, with all this uprightness and trying so hard, you MUST relax. If you become tense you have no chance of becoming long and soft in the leg, and secure.
Your hands also could do with some correcting. Carry them slightly higher, although you have a good elbow and forearm line, your hands drop and slightly turn in. Lift them and have the thumbs up to the sky and this will give you a better contact and put them in the correct position.
I am training to be an instructor so this is good for me