Ann,
The ladies have given you such great advice to ponder and pray about, and I know you are thinking deeply.

I went back through some past posts to refresh my mind about your kiddos a bit more, and I see you have been pondering this possibility for awhile now.
I'll share that whenever we're discussing possible options, we also have to consider what is going on in your life, what has happened this past year, what is ahead for you in the forseeable future, and the dynamics and levels of kiddos whom you have to teach in your home. These are the circumstances that those of us on the board can't weigh very well, but that do play a major part in how successful HOD is in your home.
With that in mind, I do think it is wise to ponder your options. If working full-time part of the year is going to be a reality for you, then that is something that will definitely affect how many programs you can pull off in the day-to-day. There is only so much momma to go around! If your older students are possibly not as independent as you'd like them to be at their age, then that will also affect how many programs are wise to attempt daily, or you won't have any time to train them in needed skills. If you aren't regularly getting school done, then it's also good to remember that often the best placement is the one that gets done in the day-to-day.
In looking at your kiddos, I know that you had shared previously that your younger little daughter had some learning challenges. This will definitely play into how well acclerating her into Beyond would go. Another thing that will make a difference is how far you are into LFHGH and Beyond. You had also shared previously that your son is fairly advanced so that is a factor as well. Last, it will make a difference what your state requirements are and whether or not you need to standardize test each year, or in what years.
With those thoughts in mind, I think that weighing all factors, if you can combine your younger two students for some things it would help your daily schedule quite a bit. The problem becomes which program to combine them within? Depending on your how your daughter is currently doing in LHFHG, it is possible that she could combine in Beyond (if you are not very far into the program with your son). If you are beyond week 12 or so in Beyond with your son though, then it may be too hard to jump your daughter forward to join him. If you are still in the earlier weeks this may be an option.
Another option would be to back your son back into LHFHG along with your daughter for only the left side of the plans and the Storytime each day. Then, you would keep him doing the right side of Beyond for the 3R's. This would be a possibility too, as long as you made sure that your son's 3R's were on the right level for him. I'm not sure whether he is doing the Emerging Reader's or DITHR Level 2/3, but he would continue with that. He would also continue with the spelling, grammar, and math from Beyond. You could also use God's Wonderful Works Grade 2 text for him with LHFHG, following the schedule for reading it in the LHFHG Appendix for your son. Then, when he headed into Beyond the next year, he could either just do the experiments in Beyond and add a higher level science text for more reading (since he'd already have completed God's Wonderful Works), or he could repeat the God's Wonderful Works text with the experiments, or he could do the science in Bigger Hearts instead of the science in Beyond to raise the level of science the next year. Any of these optoins would work. He would also move onto the 3R's from Bigger Hearts along with the left side of Beyond and the Storytime from Beyond. I share this to give you an idea of how this would work in the long haul.
Anyway, these are definitely options to consider, and I can see why you would lean toward combining if at all possible. The dynamics between your two kiddos will make a difference too so that is something to weigh as well.
Hope that helps!
Blessings,
Carrie