One thing I'll just share for you to file away in the back of your mind (until after you get underway with Beyond) is that if your 8 turning 9 year old needs a bit more in the area of language arts, you could easily borrow a few portions from the Bigger Hearts guide to customize in that area for her. If needed, you could utilize Bigger's math schedule (which includes 2A/2B with hands-on lessons in the daily plans and 3A/3B in the Appendix), the Cheerful Cursive (if she's ready for cursive), the dictation passages (if the List 2 in Beyond is too easy), and possibly Rod and Staff English 2 (if she's already had a gentle introduction to grammar).
If you did need to utilize some of these areas from Bigger Hearts, your older daughter could still move into the rest of Bigger the following year with your younger daughter in most areas and then just borrow a bit from Preparing Hearts in the 3R's.That way your girls are still together for the bulk of their day.
On the other hand, if the fit in Beyond is perfect, you won't need these tips!
Blessings,
Carrie