In which guide do the students really start doing some serious independent work? I'm getting ahead of myself; I'm completely aware of that. But since we're starting HOD with our DS(6) in Beyond for 1st and our DD(4) in LHTH for PreK, I'm finding it increasingly difficult to foresee how I could ever easily combine any of my children. I could definitely see it if we were coming into it in later years from another program or if they were each 1 year apart instead of 2, but I just don't see it working the way we're going into it. I really wouldn't want to hold any of them back (unless they have a hard time keeping up, of course), rush any of them ahead, or skip anything. SO...
Hypothethically speaking (since I realize that nobody really knows what the future holds for their family), in the future I
could potentially have:
*DS- 6th grade in the Age of Exploration and Invention/Physical Science guide
*DD- 4th in CTC
*DD- 2nd in Bigger
*AND DS- PreK -OR- Kindergarten in either LHTH -OR- LHFHG (depending on the little guy's maturity and skill level when he turns 5)
We already have the materials for Beyond and LHTH, and I'm set on doing both of them at regular pace this coming year. I don't really want any advice on combining. I really just want to know if the above hypothetical situation is even possible without poor Mom going crazy!

At those points, how much independent work would my kids be doing and how chaotic would our days be?