The last time I drew realistically, or even needed to, sadly, was in life drawing class or some such (I forgot the order of the classes). Therefore, I feel unqualified to give you any real critiques, just by virtue of it automatically looking better than anything I'd be able to do now.
I do like your work overall though, if it means anything. I like the girl with the teardrops the most and the glue-faced one (second pic), they just stand out to me in how strange they are, and I like the shading detail of the former.
So why am I here? Well, I wouldn't post if I was absolutely useless. :P Me and my good friend Loomis over here can help you with drawing hands. Some people don't necessarily like Andrew Loomis's methods, but I figure it's servicable either way. You'll want to check out Drawing the Head & Hands. Hands are the very last section of the PDF and starts on page 120 in the PDF (not in the book).