HOD is so flexible - you can definitely spread 2 guides over 3 years, and the possibilities for doing this are endless.

However, I would do this in response to a child displaying the need for a slower pace, rather than planning for it before the need arises.

If a child is ready for full-speed, it is a good idea to use that pacing (unless other life situations present themselves and make it more desirable to go half-speed, i.e. health concerns in the family, a move, a newborn baby, etc.

). Doing school 4 days a week is definitely a pacing you can always do.

So, I guess from what you've described, I'd start Beyond Little Hearts for His Glory 4 days a week, starting half-speed the first week or two to test the waters.

Then, if ds is obviously ready for full-speed Beyond, I'd go ahead and do that 4 days a week. If half-speed Beyond is showing itself to be plenty for ds, then I'd keep going half-speed 4 days a week, with an eye towards watching when full-speed fits better. Often times for us, we have switched from half-speed to full-speed halfway into the guide or so. You will know when!

Many times, half-speed at the start of a guide, then full-speed finishing that guide, then half-speed at the start of the next guide, and full-speed finishing that guide - results in 2 guides being spread out over 3 years. This past post may help as you are considering placement and pacing as well...
When to Drop Back a Guide and When to Go Half-Speed:
viewtopic.php?f=6&t=9000&p=65878#p65878
HTH!
In Christ,
Julie