Your sequence of death works with Intent to Kill, my dear Buffalo.
But why would they want to end this young woman's life, and destroy
theirr own? Was Melissa pregnant with Craig's baby, and threatening to
have it? Was she blackmailing C & K by threating to inform a) The
Authorities or b) Their Drug Suppliers? Or did Kelly simply learn
during a cat-fight confrontation with her menage mate that her
charming husband had actually AUTHORIZED Melissa's credit card
purchases. That Mel wasn't stealing from them at all. Not now, not ever.
That it was Craig instead who was betraying her. Thus, by murdering
Melissa, Ms. Fitness was destroying her entire family, and giving the
whole fitness culture a kick in the balls too.
In which case, Craig will at some point want to turn on Kelly. But
only after a plea bargain is struck to minimize her sentence, and
maximize his own publicity. Honestly, Buffalo, prison doesn't look
so bad when you're getting celebrity treatment; detox included.