I fully agree with the previous comments.
My main gripe is about the posings themselves, and particularly the neck. All of this looks pretty stiff/rigid and lacks of "life" –in other words, the human body doesn't act this way, it is way smoother. For example, in the second piece, the body of the lady looks like it was bent as a whole instead of having only its spine bent and the limbs (particularly the left arm) following it as an element made of two straight other elements.
As for the necks, it seems your characters have their head attached to the top of a rigid part and turned around, when the neck actually is a set of vertebraes which all move in conjonction, forming a smooth curve. Right now, those characters look more like some sort of action figures than living beings... Also, the right shoulder of the witch looks to be slightly wider than the left one. Be careful with the perspective of her face too, as her left eye should be closer to the line of the nose, leaving a small space between the eye itself and the side of the face.
My advice would be to find some references of the human body in various poses, preferably as photographies, and study them. If you feel like it, you could also install the free app Daz Studio and use its various provided figures as templates once posed how you want them. You could screencap the view, or make a rough render that you import in your drawing software as a basis to work from.
Keep up the good work!