No no no no noooo, kablaah. Not what I'm saying.
K.A. supposedly gave the ghosties an outline, a basic plot, and they could run with it from there. It's pretty obvious from reading the books itself that a lot of the specific dialogue etc wasn't written by Katherine or Michael. The general plot? Sure. But a lot of the characterization, the tone etc, was a little "off" under the ghostwriters. Rachel being a major one, even Marco to an extent. It always seemed most of K.A.'s writing toadies didn't quite grasp that balance with those characters that was evident in the books written by the two authors themselves. Rachel turned into a blunt unsympathetic & dangerous wildchild, Marco just being a clown.
That's not to say the general ideas for the books didn't come from Katherine/Michael, they did. But that's not my point.