Compositionally, they look fine. Maybe try a variety of compositions, IE, frame wider to get more of the torso in the shot.
For the individual shots, lighting wise, it's okay. I'd do a local adjustment, brightening up their faces. It seems a bit dark on the 2nd photo. For both the 1st and 2nd photos, it looks like you used an umbrella or similar. Try moving it in closer for both shots, especially for the 2nd where your flash almost seems to add little to no light to the subject.
PP wise, you're using Lightroom right? Drop the temperature on the slider but boost contrast via the Tone Curve. Upping the lights a fair amount and dropping the darks slightly will also have an effect on color that I particularly like. As I mentioned above, I'd brighten up their faces a bit.
The group shots great. I'd level it, it looks like you're falling to the camera left.
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