Well, the color and the rederings is ok, however the demons lack of emotions and personality, yeah, sure the're demons and they are evil, but you are only focusing on only making them look evil, you are not focusing in the sin that the demon represent, making them generic demons, if someone saw these illustrations without the tittle names, I'm pretty sure that they would have a hard time telling which sin is which.
Your mistakes are in the body gestures and facial expressions, for example, pride, his design is fine, but his posse is not, he does'nt look proud at all, he looks like has no clue of what's going on, his face should be looking happy, because he should be proud, but he is pissed instead.
Sloth, is resting is arms on his knees, but that's actually not lazy enougth too be called a sloth, he is too uptigth.
I could go like this withe rest,so, my advice is, that, next time, you should find a posse and a facial emotion that communicates the story that you wanna tell with the character.
I could point many things, about the ligths and the details of sweater, but since is a unfinished piece, I can't tell if where aware, or you did'nt get to that part, so I only will focus in the face
About the face: the eyes are very different from the sourse image, the eyes from the sourse are kind of absent minded, she looking directly but she is'nt aware about you, in contrast, with your drawing, the eyes are looking directly at the "camera" and she seems kind of aware of a presence.
the mouth is a bit small, but I guess that is a stylistic choice, however the expression should'n be sadness, I think that girl the photo is reflexive. http://prntscr.com/8cepur
Asian girls faces, are like doll's, smooth sking and no prominent features, so the shadows should be more ligth,
I tried painting over the shadows with adyacent hightligths, with a mediym opacity/ligth flow brush http://prntscr.com/8ceqct
I hope you finish this piece, it's going to look great!