Hi there Snakker here, still very much a noob so take everything with a grain of salt
So, first off, the three figures look very well constructed to my eyes, as for folds I still have no idea on those but look good to me 
So figure 1: be wary not to almond shape (symbolize) the eyes, adding a bit darker values (hair, behind the neck and left side overall will help make it more contrasty and will probably improve it a lot as is. Also be wary not to make the chin too pointy unless it's a style thing as the chin is usually about as wide as the mouth comissures
Figure 2 i think this figure works very well. The only things that catch my eyes here are the sternocleidomastoid (right could use a bit of overlap as in the figure, rather than seeming to disappear into her right curve shadow, left one looks rather curved instead of a bit straighter always starting thicker at the top and thinner at the bottom. Whenever staring hard to one side the muscle contracts and in a skinny or buff figure will be very aparent as in this case and can be very pleasing aesthetically. Also, slight underrepresentation of left trap (it's thicker and has a bit more taper toward the left shoulder. Gesture wise, left hip should probably be higher as her weight bearing leg is left
Figure 3: this looks so good! The only thing I notice particularly is the face, the malar contour suggests a much wider face
cheers! =]
