Sounds like fun!
With the caking-up thing I think, perhaps the word "children" is confusing us, because it can mean "the sons and daughters of Jack and Judy" or it can mean the ones that are in the "child" life stage...
What I understand is that before they are YA, they should all be aged at the same time, but once they reach YA, they're not children anymore, so if you want to age up all the children a second time, the two eldest, since they are not kids anymore, don't need to be aged up... But please confirm!