I agree with the expressions on the models as too "lifeless" but in terms of PP... the skin tones are too warm, giving off that fake orange/gold tan look. On the last one, looks like you forgot to desaturate the rest of her arm and shoulder. Also, on no.3, you may want to whiten up her teeth, as they are a bit on the purple side. Composition is pretty good except on no.2 I think. It's always good to have communication with them, at all times, makes them ease up a bit to where you can get them laughing, and feel more comfortable, thus, giving you much more flattering expressions. try avoiding having the models turn their heads up, under the nose shots are unflattering. (5)
Nikon D7000(with grip), D5000, Sigma 50 1.4, Sigma 17-55 2.8, Nikkor 18-200, Nikoor 35 1.4 G, SB600