I know that it is Wolfe's fault.
It is his fault for cheating on his wife.
You might even say that it is his fault for not getting a vasectomy or an orchiectomy, or at least using a condom, but of course that is far from 100% reliable which brings us back to it being his fault for cheating on his wife.
My point is that in the twisted minds of MW and may be MW's wife and daughter, everything is Ms Frettwell's fault. Imagine MW explaining to his wife that KF is a succubus who seduced him and that he "just couldn't resist." MF probably blamed KF for not being on the pill or missing doses.
I would imagine that the prospect of MW having to pay over $900 per month in child support might have inspired MW's wife and daughter to believe all of this Bovine Scatology. Mrs Wolfe joining MW in threatening to take custody demonstrates extreme hostility. MW's daughter getting into an argument with KF demonstrates extreme hostility. Once MW's wife and daughter ally themselves eith him against KF, they become potential accomplices in the abductions and murders.
If I was LE, I would be closely examining their cell tower ping logs, especially on the night of the abduction. Did they, or someone else, meet up with MF to take KF and WF, may be swapping cars, so that he could return to work while they consumated the homicides or disposed of the bodies?
BTW, I believe that KF and WF were alive when they left the apartment in Salem. If MW had killed them there, carrying a deceased KF out to his vehicle would have been to risky. Leaving them would have been less risky. Just carrying WF, may be while threatening him with a weapon, would have been suffecient threat to KF to get her to get into the car.