Alllllright
1st one:
-She has no neck. It's extremely thin, and should be 1-2 pixels wider than it is.
-Her body is also a bit small, even though she's only 15 (Since you said one age older than FE7 Nino).
-The shading on ALL of the custom parts is extremely chunky, and a little bit pillowed. All I can suggest to fix that is to reference (closly) how shading and shaping works for actual GBA sprites, probably from FE7.
-Last thing, is that she looks much older than just the one year it would have been, as you stated.
2nd one:
-The only REAL problems with this are the shading on the neck near the bottom of the neck, and the fact that you're using the FE8 outline on FE7 colors XD It's generally not a good idea to use both FE6/7/8 colors on one sprite Of course, this could be argued, but, for starting out in spriting, it's generally not a good idea
3rd one:
-His body is quite tiny. For the size of his neck and head, his body need to extend out to the right (OPV) a bit more.
-The custom shading on the top of his hair, and on his neck is done quite incorrectly. The hair:
Right here, where the root should be, is completely the second shade, and it also quite flat there. Reference some other sprites with the same facial angle, or stick the rest of Euban's hair back on.
-The neck has quite a bit of pillow shading on it. Pillow shading is when you shade as if the lightsource is sitting right between you and the part of the sprite you're shading if you didn't know. Reference some necks of similar size~
And there you go. Happy fixings.