It is perfectly apparent why Felina and Callie are present.  They serve to
completely contradict each other.  And for that matter, they contradict the
boys Razor and T-bine, because their personalites are so different and are
girls, and yet each often plays a considerable or signifigant role in
stopping the baddies.  (like using Callie as bait!)  Not stopping there, Manx
and Feral are two sides of the looking glass.  One is adventurous, in good
form, and young; the other is old, craven, and pudgy.  May I go on to say
that Abbi Sinian and Ann Gora are also opposites.  (Number one their names
are both names of cat breeds.)  Abbi seems well equipped to handle "danger"
areas, but even so barges right in.  Ann, well, just not as much, only more
annoying.
Strange that at least I, can not find the same relationships in the villains.