So here is what has been verified....
While SW was in NC with the girls, CW was pretending to be single, and he had his AP over for sleepovers for 5 weeks of honeymoon fun. He pretended his marriage was over, and asked her to help him find an apartment for him and the girls.
I do wonder now, if maybe he planned to dispose of his wife and unborn son, but keep the girls around. He could sell the house, keep all the equity for himself, and get the pity and attention for being a single father with a missing pregnant wife.
It is possible that the girls saw him killing SW and so he felt he had to go all the way in?