Welch, I submit to you that she actually DOES get it. And so does her son.
Everybody keeps giving them what they want! So they definitely "get it". They are getting it all!
And regardless of your rant to the opposite, you are actually volunteering to be their loyal servant. Some call this "enabling". Whatever name you attach to it, you are serving their hubris. The evidence is strong that you're so deep in these people's stories, with paragraph after paragraph of great detail regarding their attitudes, returns, breakages, phone arguments, lack of understanding of this or that, a true log of everything that they did. And their egos grow. Huge.
Talk to your wife about this; she's probably sick of them too. For your own health, you may want to step back a bit. Stop taking their calls for a week. Or a month. They'll get on. Or not. Whatever!
Oh and if you have made (or are thinking of making) the mistake of letting them live with you (or near you), well there's nothing that can help you until you move your keester out of there.