With respect to all who have posted some great lines of argument, I must point out an immutable fact of human nature.
People mostly decide to believe what they want, and then use logic to justify it.
You could provide a letter signed by God that says, "The JW's are a bunch of screwjobs engaging in delusions of grandeur", It wouldn't matter.
The only time direct refutations of the dubs will have any positive effect on a dub is when they are already open to it (they ask you directly or they are already having doubts).
If they are not, it only serves to alienate you from said dub.
MJ already knows this, but some things bear repeating.
The point here is not to win an argument (no reward except momentary satisfaction), but to help his wife to walk away.
That goal is not served if he alienates her with an attack on her most cherished beliefs.