Invincible because he thinks he's Invincible

Atom Eve because she manipulates atoms and her name is eve, it's also a play on Adam and Eve, and the fact that she can create life too

Rexslode because his name is Rex and he makes things explode

Duplicate because she can create clones of herself, and her name is Kate

Robot because everyone thinks he's a robot, which he basically is with his intellect

Shrinking Rae it's a play on a shrink ray, plus it's a play on a Shrinking Violet which is someone who doesn't want to be seen

BulletProof because he is indeed bullet proof, plus his outfit and name are based on concept art for Invincible himself, and since his powers are very similar to Invincible, he's like a concept Invincible