The reason your characters aren’t very distinct is because the only difference between them is their color scheme. I’d say it’s fine if you want them to be twins, or if you make their personalities very different from each other.
See the guy you did 3rd from the right? I’d say he’s probably the most distinct out of all of the other people you drew. He’s taller, has a unique design for the pants, and he has a pointier, more triangular nose.
I’d say that if you want to make characters that you think are more unique, sketch 10 or 20 something characters, and don’t have a strong attachment to any of the sketches you made. Pick the traits you think are the most appealing and try and see if you can make a few of the traits from each work on one or two characters.
Also try getting some reference for body types, clothing, hair styles, hair colors, anything that you’re willing to experiment with your characters. Try sketching your favorite findings.
I hope this helps!
Anonymous-Frog
Some suggestions:
1. Change the hair shape.
2. Give them smaller eyes, different shaped face (ie. more pointy, square, etc.)
3. A hat
4. Make them slightly shorter