BD1, I think your theory of what happened initially in that MBR to launch the murders, etc., is very logical and it's the most reasonable one of all.
As I've said before, it would have pizzed me off to go & find my side of the bed wet -- especially if it had been my 5-year-old. That it was the older child, who should have been old enuff not to wet the bed, would have made me mad at the child, and it would also have angered me that her mother should have taken care of that problem (in Jeff's "male dominant" mind, that was her job and she had not done it). And, for all we know, this bed-wetting by Kimmie may have been a frequent problem.
Jeff had been working three jobs, had been up for over 24 hours, was tired -- I'll give him that. It was the last straw of possibly a tuff day, and Collette leaves him with the girls while she goes to class, so he now has that to do -- and if he had taken an Eskatrol a little earlier, it probably exacerbated the situation .
He certainly could have ruffly awakened his daughter and struck her, as you suggest. Then of course Collette, who isn't the happiest mom of all time by now, does what she can to stop it.
He is just plain guilty, and his totally intentional murder of little Kristen is the cruelest type killing imaginable.