C.W., have you checked out the work of Steve Pyke? I've found his work to provide a lot of inspiration in how to compose and frame the face in a simple yet powerful way.
When it comes down to three-quarter length portraits things can get tricky with hands and such, and its important to get these things looking exactly right.
With the girl portraits at the bottom, I would've liked to have seen a straight-on portrait with her face resting on her hands gripping the chair-back. Your photos have made me see this, and maybe it could work. Just an idea.