I have been following this case since the beginning and I think Chris is the type to internalize his rage. Chris is a Beta male who probably feels inadequate due to both his mother and wife (both of whom are Alpha's). He may appear easy going and non-confrontational but deep down is seething with resentment towards the women in his life. Shanann and Cindi probably didn't get along because they're both Alpha's and Cindi treats Chris like a Momma's boy who can do no wrong. Similar to Scott Peterson, we have a golden boy who is worshipped by his parents.
I feel he'd intentionally cut himself off from his wife and kids. He didn't want to be attached to them in any way. He has NK who is probably younger and a bit naive. NK will follow Chris's lead and Chris can't believe he has a woman who will do what HE says but there's that pesky, pregnant wife of his who won't "go away" quietly because understandably, Shanann loves Chris unconditionally and is willing to work on their marriage. I also feel like Chris felt backed into a corner with baby Nico in the way.
So what does an emotionally immature Beta male do when he wants to rid himself of his family without paying out big $$$ for a divorce and child support? Just snuff them out plain and simple.
Chris is not smart or clever, nor is he a good actor. There is no way he was going to outsmart anyone by pretending to be the grieving husband. Chris is a dumbass who felt that he could go about life without a care in the world . Chris is a product of his parents (who btw seem pretty evil and narcissistic themselves). He honestly believed the police would just shrug and say "Yep, you're right Chris. Shanann probably just left without a trace. Oh well".
My guess is the kids were in bed, Chris is anxious for Shanann to get home from the airport. Shanann gets home, exhausted, feeling ill and pregnant. Takes off her shoes and gets ready for bed. She probably peeks in on the girls but tries not to wake them. Chris is probably pretending to be asleep.
Shanann gets into bed and gently tries to wake him up and whispers "Chris .. honey ...I'm home."
Chris probably lays there ignoring her while pretending to be asleep. Shanann tries to hug him and maybe he pushes her arms away. She says "**** off" and rolls over, maybe crying until she dozes off.
Then Chris probably rolls over, sits on top of her and strangles her first.
Then the girls. My reasoning is because he can't take a chance of Shanann discovering the girls are already dead and having her call the cops or cause a disturbance. He kills her first so that he has ample time to smother the children without Shanann interfering.
My other scenario is Chris pretends to be asleep in bed when Shanann gets home. She climbs into bed, and he rolls over and pretends to be loving by wrapping his arms around her. Maybe even says some loving words like "I missed you. How was your trip?" They chat like this for a few minutes until Shanann dozes off. Chris pretends to do the same.Then, with his arms still wrapped around her he strangles her. Shanann didn't have time to scream or fight back. Because of Chris's loving demeanor, Shanann, already tired from her trip, let her guard down and didn't want to to think about Chris's strange behavior the past week. She's dozing off when Chris decides to go through with his plan.