Well, if the familiy's objective, after the event, was to keep everyone out of prison, the son's text to CH practically guaranteed that they both WOULD go to prison, the only possible qualifier being that the son's texts implied pressure. But not to the extent of the legal definition of marital coercion.
Even in the recorded phone call you can see that what CH is doing (clearly aware of the possbility of recorded calls) is saying that it didn't happen and that VP should say the whole points-swap was a malicious press rumour - a tactic which would, again, have kept them both out of prison. She of course was doing the same thing to some extent. Trying to 'nail' CH while escaping her part in it - lying about the aide and then claiming marital coercion.
Morally of course CH is the worse because he did the crime, sought to escape the legal consequences of his crime and lied on the form saying his wife was driving. And then continued with cynical tactics as decribed above to try and maintain the lie and escape justice. .
But the law is the law, not the Jeremy Kyle show or The Moral Maze, and it seems to me that they have both viewed the justice system as an expedient means to their own ends. Him to drive as he likes without sanction, her to use it as a way to avenge her ruined marriage. Both have been caugt out. Boo hoo.
And frankly, though I sympathise with the children (who wouldn't with those parents) , the son, who is intelligent enough for the higher education he enjoys should also have know what he was condemning his mother to when he sent those obviously consciously incriminating texts, saved them, and offered them as evidence.