John's Mom,
Thanks so much for sharing more about your kiddos. It really helps, and I am grateful you were kind enough to take the time to enlighten us!
From what you've shared, with all combining scenarios aside, it sounds like your daughter would fit best into Little Hearts for His Glory and your son would fit best overall in Beyond (with the addition of upping a few parts of language arts and math).
Since your daughter does listen in well to chapter books, she could definitely listen to the material in Beyond and likely could participate in most of Beyond. It is also fine for her to still be doing phonics while doing Beyond, however the writing would be one area that will be tougher if she's still learning to write her letters. You have a great plan to begin working on her manuscript letters now so that she's ready to write words in lowercase letters by the time she heads into Beyond.
I'm not sure of the ages of your kiddos, which will make a difference in their best long-term placement based on their age in relation to the maturity of the content in the material. So, I'm assuming in these scenarios below that your daughter will be 6 in Beyond and your son will be 8. If I'm incorrect here, definitely correct me.
When combining your kiddos within Beyond, I'd plan to use a handwriting workbook for your daughter (likely A Reason for Handwriting A or its equivalent - which includes copying words each day and copying an entire short verse once a week). It sounds like you have your daughter's spelling, reading, and math covered, so she'll be fine there. You may wish to make next year your big push year for phonics with your daughter, in order to help her be ready for the Emerging Reader's Set by the time she gets to Bigger Hearts.
When combining within Beyond for your son, you'll want to add on your own higher level of handwriting for your son (something like Cheerful Cursive or its equivalent). You'll also need to add in the Rod and Staff English 2 from Bigger Hearts, but because you have your own spelling program and math program, you won't actually need to purchase the Bigger Hearts guide (as you'll be upping those areas automatically on your own). Rod and Staff English 2 should be done daily in order to finish within a year. The lessons are already divided daily for you. Do much of each lesson orally requiring only a small part to be written on paper each day. English 2 is appropriate for a third grader, as the sequence of Rod and Staff is quite advanced in the area of English.
As far as reading goes, I would recommend beginning your son in the middle of the Emerging Reader's Set (around Prairie School or so) and continuing on to the end. According to the link you sent above your son is reading at the 2.5 - 3.7 reading level and our Emerging Reader Set is in the 2.4 - 3.4 reading level, so it should match him very well. By beginning in the middle of the set, you will be beginning at his reading level. It will be very important to ask the included comprehension and narration questions in the Emerging Reader plans for each day's short reading (in order to make sure he is comprehending and is reading aloud well). Then, after he completes the last half of the set, he will be ready to move into Drawn into the Heart of Reading Level 2/3 to finish out the last half of the year.
Normally, we'd also recommend doing the dictation passages for spelling within Bigger Hearts (for your son). However, it sounds as if you have that area covered within your current spelling program. If I'm not correct, then you'll need to add in the dictation for your son as well.
You can plan for an adjustment period when your kiddos move up to Bigger Hearts the next year, however you can always go half-speed when you get to Bigger Hearts to ease your younger child into the program if needed when you get there. In this way you can keep them together for the long haul!
Blessings,
Carrie