This is great! I really like how you can tell their personalities in this artwork. I've always wished JK Rowling would've said more about this group that was probably a Slytherin counterpart to the Marauders, but at the same time I like how it leaves a lot of room for different fan interpretations.
I'm glad you decided to include Bellatrix. Most fanfics and fanarts portraying Snape's gang tend to leave her out due to JK Rowling's Black family tree giving her a DOB of 1951, but I still prefer to think of her being closer to Severus's age as was originally stated.