As much as I disagree with pretty much everything else Kev is doing, I don't see anything wrong with him telling his daughters the truth, in an age-appropriate manner. I'm a huge proponent of kids shouldn't be lied to, and if one partner doesn't want a divorce, I don't believe in giving the kids the illusion that both parents are in favor of it.
There are ways to do this respectfully, and I think he did that, and there are even ways you can include the validation in it that you're talking about:
"We need to respect that Mommy feels this way, and that this is what she wants. I don't want it, but it's OK for grown-ups to disagree with each other sometimes, even about important things. I still love her very much, and I know you do too, and she will always be your mother and we have to respect her. Do you understand?" (or some such).
Many adult children of divorce report of having issues of being lied to, and I don't think it helps at all.
