I 100% believe CW killed his whole family. His claim that SW killed the girls seems ridiculous to me, based on what we've seen and know about SW, the details he included don't seem accurate or likely, his reaction to her supposedly strangling them is nonsensical and implausible, the great lengths he took to cover up a crime implicate him further than what his story suggests, and on and on. But...I've watched his interviews a few times now and some of the things he says - specifically, the things he says regarding his own feelings - I don't know. They seem to have a ring to truth to them. And that's what confuses me.
There's some major dissociation going on. He says three times in one interview "I don't feel like this is even real right now/It doesn't feel like it's real/This doesn't seem real at all." Three times in the span of a few minutes. There's some psychological distress there, possibly some shock, but mostly it sounds like disbelief and denial of what happened, which I think would be less likely if the events were planned out. In another interview, "It's not something I can even fathom in my lifetime" and "It scares the living crap out of me right now just knowing that it's come to this." Then, the multiple mentions of it feeling like a "ghost town," and that staying in the house was "traumatizing," and that it felt like he was "living in a nightmare." It doesn't sound like remorse or regret to me, per se, but it sounds more like a violent episode escalated and he felt (for whatever reason - here's where logic completely fails me) he had to see it through to a terrible end.
Maybe I just can't let my brain go there; maybe it's wishful thinking. But I struggle with believing with confidence this was premeditated in a planned for weeks/months in advance kind of way. I don't know that he just snapped, but I do question if his actions went farther than his initial intentions. It seems like he almost shows some emotion when he speaks about his daughters. Not so much SW.