I think the subject of background light for separation has been covered, so:
1. Watch out for hand placement that is intrusive. I find the large white palm of her handside to be distracting. Look at that shot and visualize the hand not being there. We are free to see her beautiful face without that competing element. You got great catchlights in her eyes and a great expression!
2. I always find that type of leaning on the elbow to result in a very awkward arm bend. Picture her leaning forward a bit with that wrist resting on her knee. Also, watch out for the shoes and how that those white soles protruding into the foreground grab your visual attention away from her. A different posing of the lower body or even barefoot would be a bit better? Maybe, I don't know, but the shoes are killing an otherwise reasonable pose.
3. Better, but shoes are killin' me once again. Still, you got a very natural expression and a bit of shine on her hair, nice.
4. This is a classic pose and one that is often done incorrectly because feet are often growing out of heads on this shot, but you did the proper thing by having them angle them slightly away from the heads. It would have been better (??) if they had BOTH been angling feet away to camera edge instead of one girl angling in, and the other out. Minor point, but it is all about the details. Also, removing the shoes would have been a happy. Bare toes suit the casualness of this pose and would eliminate the issue of viewers looking at the dirty soles of the shoes.
Also on that last floor pose, I love the symmetry of both girls putting their hands up the same way. However, the girl on the left has such a discrepancy in skin tone between her hands and face, it might have been better to fix that in PP, or choose to put both girls hands down away from the face. Again, minor points, but you did a great job with getting great expressions out of them, even lighting, nice composition, etc., so you might want to consider working on the details, if you agree with my point of view in that regard.