Not to accuse them of being dishonest, but it also costs them nothing to say that, loudly and often, in a political environment where they know it's not going to happen.
These are private and personal discussions, ranging over many areas of politics where we disagree and agree. I have no reason to doubt them. Even with a massive tax eliminating inheritance, their children will lead charmed lives. They are more afraid of a dysfunctional family than their children suffering from material wants.