Janet and Terry blame Jack for lying to them about the pregnant woman...but it was Larry who made up the lie. In fact, Jack..."in character"...even says "it must've been" the only thing he could've done [driving the woman to the hospital in Janet's car]. So, finding out the woman wasn't pregnant shouldn't have triggered the girls to think that Jack told the lie...but that Larry did.
Jack, who pretends to have amnesia, tells Janet and Terry that a nap will help regain his memory. But after his nap, he still pretends to have amnesia.
Janet disciplines Jack for lying to her and for driving her car without her permission and then getting it wrecked. But she doesn't discipline Larry, even though, he was one who talked Jack into taking out her car and he also lied to Janet.