Schweser Claw-back provision twice, provision, children, original

cyber21

In SS4, Estate Planning part of Schweser (Book1, p258), there’s a simple example about the “claw back” provision and I just can’t seem to grasp it for some reason and can’t find it in the CFAi text with a similar one.
Could someone please explain this example to me? Why is the estate divided by 3 twice? Since the two original children already have $2,750, why doesn’t the third child just get the remaining $500?