LeAnna,
I'm so sorry if I've managed to confuse you!

I'll try again with a hopefully clearer explanation.
First off, I'm having a tough time remembering whether your kiddos have already done LHFHG or not? I'm thinking that they have, and are just going into Beyond.
If that is the case, then the only reason I recommended half-speed as an option is to give your 5.5 year old a chance to grow up a bit. You could also accomplish this by doing the plans at full-speed 4 days a week instead, if you think your little one can handle the full-speed pace from the beginning. Either option will allow her time to grow up a bit before getting to Bigger Hearts.
Next, as far as The Reading Lesson goes.... Since your younger child will still be finishing up phonics while beginning Beyond, you could either wait to start her on Spelling List 1 (until she's through the Reading Lesson), or.... if you feel she can write pretty well and is ready for spelling list 1, you could begin it when you begin the Beyond guide.

Your older child will start spelling right away as scheduled in the Beyond guide.
As far as the poetry copywork goes, your older child will do some copywork from Beyond daily as scheduled. However, your younger child may or may not be ready for copywork. If you think she would benefit from another year with a spelling workbook, like A Reason for Writing A or Italic B, then you could go that route instead for her handwriting practice. Either way, both kiddos would still do the poetry lessons each day as designed in Beyond.
For the Emerging Reader's Set, you would begin your older child on it right away when you begin Beyond. Then, whenever your next child finishes The Reading Lesson she would begin the Emerging Reader Set after that.
Is that any clearer? Please let me know if you have other questions.
Blessings,
Carrie