Readers do notice, for what it's worth. I flipped to the front cover and tried to figure out who was who as you described them. And while I did figure it out--except for the blonde, it was more from clothing and such.
And... horridly I can't remember which one, but I think it was Talia... I also expected one of them to be more curvy/sturdy... ...and for Snow to be a touch more busty. (Though I can see not wanting to fall into the busty/comicbook mold.)
Physically, I think he did a little better with Talia on the cover for Mermaid's Madness
. Her arm and shoulder in particular look more muscular than on the first book.
As for Snow ... yep. I think my comment to the editor was that I REALLY didn't want a "Chain mail bikini babes" cover, but if Snow was showing some cleavage, that would probably be appropriate for her character :-)