Hi Stawna! Nothing to worry about here - when your 6 yo finishes Beyond, you'll just move her up into Bigger Hearts. If she needs a bit of time to grow into it, you can do Bigger Hearts half-speed for a bit.

When your 9 yo finishes PHFHG, you'll just move him up into CTC. If he needs a bit of time to grow into it, you can do CTC half-speed for awhile. As far as his math, when he finishes the level he is in, you can just move him up to the next level, and the same goes with his grammar. This will work just fine!

Just be sure to do each part of the plans completely with each of your dc, and they will be ready for the next guide. HOD guides are written for a range of ages because all dc are different in what they can/should do at a certain age. So, Beyond is not really a "first" grade program or a "second" grade program, but rather just a guide to be enjoyed with dc who are needing those skills.

Set your worries aside and just thoroughly enjoy Beyond and PHFHG - HOD has you covered for the rest of the years to follow. HTH!
In Christ,
Julie