Let me see if I've got this all right...

There is one G2 Male body that all 4 males share.  There are 3 different heads, due to Simon's head being a morphed James G2 head.  
This means that their bodies all can share the same textures (and morphs) BUT only James and Simon can share the same head textures (and morphs).  Koji and Kelvin each have unique heads that require their own separate textures (and morphs).

There is one G2 Female body (except a minor issue with the neck) shared by Sydney, JessiG2 and the upcoming OliviaG2.  This means that their bodies can share the same textures and most of the same morphs (RDNA isn't charging extra for the morph modifications and they're so slight that its basically irrelevant).  All three of the G2 women have unique heads that require their own textures and morphs.

Miki 2 is unique and NOT a G2 character.  She will have her own morphs and textures.

Despite all this I must admit I'm really beginning to like these characters and finally I think CP has got this latest release of a character right.  Lots of texture packs, lots of clothes and lots of support... all for a character I didn't have to pay for :)