I mean I am no pro or anything like that so take my critique with a grain of salt. First the good, you did a good job not going of the rails with drastically different shades and the proportions are ok. However the faces lack a definitive light source, this is mostly noticeable in the shadow that usually casts from the nose depending on the light source. Look up some references of strong light sources like outdoor pictures and study how the light affects the face.
The eyes are a little too big on both subjects, I sometimes do the same thing its like our brain is telling us that the eyes are important and we want them to stand out so we draw them bigger than they need to be ( STUPID BRAIN). The transition from the front of the nose to the sides is a bit too strong, a softer transition like the one you used on the bottom of the eyes would be better. The only way you would get such a strong transition is if there was a light source shining directly on the face and it probably would only show the strong shadow in one of the two sides of the nose. The side on the light would get gradually darker as it fades back but it would be a much softer transition. I hope you find my critique helpful. Lets keep growing as artist 
and keep rocking that stylus.
