I can't explain this feeling I have. And please don't call it an instinct. I don't believe people have instincts, just animals, fish and birds. (and don't post and say I'm wrong about instincts. We don't have time for that on this thread).
Anyway, I do not believe this murder was premeditated. Too many goofy and careless mistakes from someone who should know more about crime both how it's committed and how someone gets caught.
To me, this started as a raging argument sometime during the evening and turned into a physical fight and finally a murder. There are so many things the Colemans could have been fighting about.
Perhaps she learned about the other woman. Or that he'd been lying about everything from the threats to money problems.
A fight that got physical and he took it too far. I know we don't have any evidence so far of her being injured outside of being strangled.
Then, because she was dead or close to death, he had to get rid of the prospective witnesses. And, I don't think killing the boys was something mentally easy for him. But weighing the choices he had, it was something he had to do.
I think Coleman went into a mode of covering this crime in a haphazard method just grabbing from his mind whatever he could to cover what had happened.
He left the home after writing that on-the-wall message ( an act of desperation he thought would help point the guilt elsewhere). And put himself away from the crime and arranged for someone else to find the bodies. That in itself seems like a spur of the moment plan. Almost like OJ getting his butt on a jet to Chicago.
There you go. That's what I'm thinking - and I'm sticking to it until more evidence is uncovered.