This is my first time posting here. In the fall my four children will be 7th, 5th, 4th, and 1st. I have decided to switch to HOD for the three youngest. Up until now, I've pulled my middle two along with my oldest and that is just not working----she is too far ahead, and they are not getting what they need. It's time to divide them up.
Preparing looks like a good fit for my 4th/5th graders (they both have some special needs.) Beyond looks perfect for my 1st grader----she reads chapter books fluently, just finished Singapore 1B, and writes well.
I was not going to use HOD for my advanced soon-to-be 7th grader. However, I am starting to consider Revival to Revolution. It fits where she's at chronologically in history. She loves history, loves to read, loves to write. She works well independently. And RevtoRev just looks really GOOD.
However, that would mean that I would be doing THREE guides. All of my kids are solid readers. They all enjoy school and work well independently. I enjoy organizing and scheduling, however, I do like to keep things as simple and streamlined as possible. Would attempting to do three guides be crazy?? How much hands-on time would each guide take?
Jen
We have found that as long as dc are appropriately placed, running 3 guides is not hard to do. I would try to forget about the historical time period and look at the placement chart with just your oldest in mind to see where she best places. Printing off the first week of plans of the guide you think she places in best and reading through the "I" independent boxes to see if she is able to do the reading, the writing, the activities, and the step-by-step directions independently will help you know if the guide's a good fit for her. It sounds like your other dc are well-placed, so just the oldest is the one to ponder! 
You'll find that once you see how HOD works it becomes very easy to do multiple guides over the years. In fact it gets easier as they get older.