Posing subjects with the hands near the face, as in each of these shots, can present problems. Often, the hand is SUCH a different color (or even texture!) than the face, it becomes a visual distraction. Or, the subject looks uncomfortable or unnatural with the hand up like that. I don't think the hand pose was the best choice here for your young and beautiful subjects.
Having said that, I loved the colors in the first shot, the shallow depth of field, but would have cropped a bit looser maybe and angled her shoulders a bit and kept the hands out of it. I love her connection with her eyes to the camera and her natural expression. Awesome.
The second shot: I loved the pose (not the hands up though) because it was suitable for a young girl, casual and youthful. Watch posture on your subjects, you will constantly have to remind them to straighten their backs. Angling her entire body slightly and bringing her face back to the camera would be flattering too, rather than straight on. I like your slightly higher camera angle on that shot as well, and that you had some foreground blur, but the background scene was a bit messy. Still it was suitable for a young girl. AND you didn't get glass glare!!!
The third shot: This was the most successful in terms of the hands up, but still think hands away from face would have been better. STill, you stair stepped the fingers, kept the hand well back from her face, and framed her face by having her other hand touch her elbow, resulting in a much more natural "hands up" pose. I love the framing with the blurred leaves and the composition to the right of the frame. If you have room to crop more, I'd probably do that, keeping that same composition. Fewer leaves, more pretty sister.
You did well, I hope your sisters are happy with them! And you've only been shooting for a year? Great job!