I'm not going to go in full-theorist mode cuz i'll get roasted like a roasty toasty mellow marsh. idk everything is opposite... (i'm only putting what i observed)
Cynthia's legs are apart, Lusamine's legs are crossed. one wears black, one wears white. They both have a different hand on their hip. Their bangs cover opposite eyes. When they have their hands on their hips, the outside part of Cynthia's hand comes in contact with her hip, while Lusamine's palm make contact with her hip. Another thing is that Cynthia's head/face is longer than that of Lusamine's. Lusamine's is more round. I'm not much into genetics but it might just have something to do with how far the generations are from each other in the timeline. Cynthia is tanner than Lusamine and could resemble something between light and dark. Cynthia wears black but is really nice, and not mean as people stereotype black to be dark and evil. Then Lusamine, based on her behavior in the storyline, she wears light but it doesn't seem much so until the climax of the plot where everything changes.
Similarites? They both have a gem-looking thing on the chest part of their clothes. Both are blond.