These are lovely portraits and I really dig all the different expressions here. And theres so many! If you want to take these to the next level, if might be a good idea to take a step back to understand values. You want to keep it simple to start. Just restricting things to 5 values is a good way to start. 2 values for the shadow, 2 values for the midtones and then 1 lightest value for the hightlight. Keep the shapes as simple as you can and think about the biggest shapes first. You dont need to worry about details until later. Thinking about the planes of the form will help. Planes facing away from the light source shouldnt be brighter than the planes facing the light. Considering all these things will add more sophistication to your artworks and create more convincing illusions. I included an apple demo to show a simpler version of the same project. It’s the same concept, just simplified down even further.

Great improvement from your first attempt! I wanted to share this value study tool with you: https://www.proko.com/values. It's a great way to flatten the image and find the value shapes. You can get a similar effect by squinting your eyes. When you do so, the areas in shadow appear to be around the same value in places at the hair. I would simplify by dividing the face in half by light and dark values, so the majority of the light values are on the left side and the majority of the right side is made up of dark values.

Nice! those are great gifts, look forward to what you create with what you learned with this course! :D