Shading wise, they are perfect. There are some sharp ones, bold ones, and also smooth ones. That's the way you would want to shade in the future. You probably still need to work on the facial shape in the future, but since this is a shading study, it's not a problem for now. About the shadow being too light, from what I see, it's a problem at all, since when it comes to shading, what matters is relationship between the light and the shadow, not the actual darkness or lightness of the shading. A good measurement to tell if your shading is in the right place, is to squint your eyes and move away from your drawing about a meter. If you still can clearly see the separation of the light and shadow, the you're in the right place. Have you ever tried to use a dedicated art model's portraits? Photographs from google or pinterest may look great, but most of them are heavily edited, and are not particularly designed for artists learning. From my experience, by using art model's portraits, learning shading and/or structure will be much easier because 1) it's not edited, or even if it is, it will be extremely minimal, 2) the photographs are taken most of the time by fellow artists as well so they know what's specifically good for artists, 3) it uses the same model over and over again, so you can stay focus learning and being familiar with one face only, but from many angles and lighting condition.