Advising the Newlyweds
Jonathan needs to walk a fine line between helping his newlywed daughter and son-in-law and insulting them.
Dave's ANSWER: You take him aside over some coffee or a field trip somewhere and just talk to him. Tell him you don't want to interfere in their lives and that he is the man of the house, but you've been down this road and paid your share of stupid tax.
You see how much pain they are bringing to themselves. You don't want to interfere, but you do want to help. Offer to buy Financial Peace University for them, but tell him that you aren't going to your daughter because this guy is the man of the house.
I've got a couple of married daughters, so you must be careful as the father of those daughters to not neuter the son-in-law. Daddy still has this girl's heart, and you can step in there and do that. Keep setting him in a place of honor and call out his manhood, just man-to-man rather than father-in-law.
Depending on the quality of kid this is, you may be able to pull that off. But you can't do it in front of your wife or his wife.