With everything we've seen, I'm really leaning heavy into the "Momoiro didn't murder his wife and daughter" theory. I'm watching the anime with one of my friends and I couldn't help but notice how dense the blood stains on the wall are. Those don't look like precise slashes, they look like something blunt and brutal. I suspect he came home to find his work buddy had killed them and when the Kougasaki formerly known as Momoiro returned, the work buddy was still there so he had to "kill" Jin.
He's way too precise with his powers to make a mistake like that. Being able to cut JUST the oxygen, based on the lack of wounds on Kougasaki? Crazy work, no shot he messed up that bad by accident. I feel like he's playing the villain here, at least to some extent. It'll be interesting if we ever get a glimpse into his inner thoughts, but that probably won't come until we actually get the climactic father/son fight.