Yay! I think those last two are very nice!
I think you caught the expressions well and the shape of the head looks much much better.
There are litle things to nitpick on, but I think you drew them nicely!
Now here are the nitpicks;
- On the "americana girl" the mouth looks like it's seen from the direct front, while the rest of the face is in 3/4 view.. Also the upper lip is much thinner near the corners of the mouth. The hair is something to work on too because I see a lot of lines, not hair. I know it's hard to get hair right (I struggle with drawing hair a lot myself), but the advice I've gotten from people is to divide it in to locks, and only draw those, so draw only the outline of the hair and a féw locks. That's the base.
- On the last one this hair crit also stands. About the eyes; Do all of these girls have make up on (to make their eyes dark on the bottom) or is this just the way you draw them? I suggest you take a good look upon some eyes (wait, I'll just post them here
As you can see there's this little light fleshy line below the iris (above also but you almost never see it well), I don't know what it's called, but I think it's kinda important to also draw that little line, because I think it makes the eyes look much more real if you have that in your drawing.
Maybe you can do a page with just a lot of eyes drawn? You can use a mirror and your own eyes as reference material or find pictures/ drawings of eyes on the internet.
You can do this too with noses, mouths, ears, whatever
Oh and just one other thing; with shading you can go a lot further than you've done so far, really push the values and get some darks in there also! Even if it's not in the picture, you just find the places that seem darkest on the picture and make them a bit more dark in your drawing. Don't be scared to draw shadows in the entire face, it probably will go wrong a few times, but you're not here to make these beautiful drawings, you're here to improve and experience right?
Enough nitpicks You're doing great! Keep it up!