I have a two-fold question, I think. We will be switching to HOD in with our new school year and I am super excited!

A little background ... my oldest will be in second grade, turning 8 at Thanksgiving. She has completed MFWK and is in MFW1, and we are very happy with her progress. Aside from MFW we use FLL1, Singapore 1A&1B (completed Miquon Orange), Calculadder, Draw Write Now, Classical Kids, and we have been reading storytime selections from Ambelside and Mater Amabilis. She is more than ready for cursive. We have not used a spelling curriculum, but she is a good phonetic speller and we do some dictation daily ... from words to one or two sentences. I think that she fits squarely in Bigger, but I'm sure that she would do well in Beyond, but she may not be challenged enough and I would rather slow down the pace of Bigger than beef up Beyond. To be honest though, I am not totally sure since I can't say how MFW has prepared her for HOD, or if that matters at all, since her curriculum is more than simply MFW.
Thoughts on my thinking there? Anyone with MFWK and MFW1 (or similar) kids who moved to HOD ... was Beyond or Bigger the better choice?
My middle two are 5 (as of two weeks ago) and 5 (6 in July on paper, but he will be aged a year younger ... adopting from Ethiopia). We are planning on LHTH with both of them and MFWK (I think that MFWK will be better suited for our adopted son and I already own it and was happy with it the first time around).
My youngest is just tagging along at this point. I've decided to wait another year or two for LHTH for him.
Given my Kinders, and my oldest, I would love to possibly get them in the same year at some point down the way here. I absolutely see the value in teaching separate guides and proper placement is of utmost importance. That said, I would still like to explore if there is a way to get them in the same guide, with extensions for my oldest, while preserving their placement.
I was roughly thinking (and I apologize in advance if this is just a ridiculous wondering) ...
What if I put my 2nd grader in Beyond this year and my Kinders in MFWK (for our Ethiopian, his year will be modified to suit his needs first until he is learning the language and ready to really learn ... no pressure for him at all--just life, family, settling in, and good books to look at first--then "school", but historically, our adoptive friends' children cannot wait for school! It is such a privilege where he is from so they want to be a part right away, and he'll have been home 3 months before we start the school year. I will also do LHTH with him alone in the mornings).
Then, next year, 3rd grader in Bigger at half speed on the left side and full speed on the right, and 1st graders in Beyond.
Then, 4th grader in Bigger at half speed on the left and full speed with 4th grade options on the right, and 2nd graders in Bigger.
Then, 5th grader in Prep with extensions, and 3rd graders in Prep as well.
So on ...
The two big drawbacks I see to this hypothetical are that my oldest won't get to Modern History by 8th grade and she'll miss Geo thru History, unless we did that for 9th grade. Also, my middle two will never have done LHFHG, but will instead have done MFWK (and LHTH to ease our adopted son into school) and then to Beyond for first. Not sure that this is really a concern, but throwing it all out there.
I know that this is looking far down the pike, but I like to have a map in my mind of where we are headed, especially before I click purchase.

Thank you for reading so long and for helping me along.
I am blessed already by this board.