Hiya! Nice job on a lot of those. A few constructive criticisms. Now, keeping in mind I know NOTHING about spriting, I'll just comment on the general look of things.
Marle: Her pants seem a little too baggy and almost look... I dunno... wrinkled? Also, her and Ayla seem OBSCENELY thin.
Lucca: The problem is that you simply can't tell if there's a guy or girl under there. maybe make the hair protrude a bit more? I dunno. I also remember the glasses being larger in the original sprite, giving it a more anime look, which i liked a little more.
Frog: Looks a little odd. The face seems to thin, definitely.
Magus Looks... Cute. Cute? magus is not supposed to look cute! He's supposed to be foreboding. Ominous. Scary, even. This was a guy who terrorized humanity in the middle ages! I looked at the original sprite. The ears, I think, are too big. I think they need to be made smaller to emphasize Magus' humanity. His EYES, on the other hand, need to be deemphasized to emphasize his inhumanity. I'd think that'd probably make a better Magus on the whole. I also think he's a bit too colorful. I think his clothing should either be darkened or be shrouded a bit by the cape. Also, HE WEARS A CAPE, for god sakes. Use it. Make it bigger. Scarier, have it give him the illusion of mass, cuz Janus is a small guy, you'd think. Or bulk him up a bit. He looks WAY thin there.
Pretty awesome jobs on Ayla (minus the waist), Robo, Crono, and the Cross Crew. I look forward to this project quite a bit.
Now, back to lurk mode!