I get what you are saying, cityslick, but (how do I say this tactfully), I don't think that either of these parents are that swift. For all we know, JI has since taken the PG and has failed it. If he did, we would NEVER hear about it because, LE isn't talking to the media and the DT would absolutely keep that a secret. On the other hand, if he took it and passed it, the DT would be shouting it from the rooftops. There is no doubt about that.
I think that DB is one of those people who has a problem with lying/drinking and being a drama queen. She also watches a lot of missing children's cases, per her statements. I think that she knew that for her to deny a PG, it would look really bad. I actually think that she might have convinced herself that she could pass it because people with narcissistic personalities (which I believe she has) often feel that they can do things that others can't. That, coupled with the fact that she is not all that bright, makes me believe that she was probably surprised that she wasn't so convincing that she had passed it.
And, before I hear the comments about "how smart" the parents had to be to get away with all this...remember that it doesn't take even a median IQ to commit murder or, even less, have an accident occur.
I think that the accident happened, the two of them set it up between themselves, staged everything and made "D Day" be when JI came home from his night job. That wouldn't take any brains at all. All it would take is for them to stick to their story and act upset.