While that one guy with the tall head was intentionally silly, I think I’m struggling most with proportions. I’m using a reference image for most of these, but none of the end results look much like the people in the photos. I’m also not using a grid as I’m doing this all with pen. I know I’ll eventually get it with practice, but is there anything specific I could try?
A “feminine” look is a lot of facial features coming together at once. Face shape, Hair, jaw, eyes, etc.
Focus on getting each detail right and that will come together.