The power snatch, and the power clean, for that matter, is generally held to be executed with the athlete descending into no more than a quarter squat to catch the bar. This means it must be pulled much higher, which is the goal of the power versions of these lifts: increasing skill specific pulling power.
On the overhead squat, for me to truly judge, the camera angle needs to be better. It should be in line with the hips, and it looks a little forward, but it could be the angle. Camera should be straight in from the side.
If at first it feels like you are going to drop the bar in back of you, it is probably correct. It is very important to arch in the bottom. This recruits the hamstrings, and allows them to assist in the drive out of the hole.