The line art clothes studies look pretty good. The grayscale does help with the shading and clothing folds. The references, combined with the other figures, do look okay. One thing I can think of is adding more shading to the clothes.
Okay, I found this one. It might help.
And this one at the 3-minute mark could help. Both are from Pikat:
Another one that comes to mind is Draw Like A Sir:
Hello, you're doing pretty well with the primitive studies, especially with Mr Frog.
Your anatomy studies are pretty accurate.