This is a great start and I can see these working in a GBC title pretty well.
What these sprites need is less detail, to use the small canvas space to their advantage.
Right now they have space marine syndrome, basically all armor on the hero team looks the same. It's pretty hard to distinguish between each character at a glance.
But the detail is the second biggest cause of that, first is probably color identity, right now these go from black to white without a lot of green or red or whichever.
Focus on the big shapes, or clusters as they apply here.
Also use a shadow color other than black as long as it fits into the GBC 15-bit colorspace.
All 3 colors should have value but also have identifiable color properties, see those up there for ideas on how to do that.