HOD and Ambleside do share a love of CM methods, but I too have enjoyed the structure HOD provides.

I agree that from what you've shared, LHTH would be a good fit for your younger, while Beyond would be a good fit for your older. We did both of those HOD guides last year (along with CTC for my oldest as well), and enjoyed our year so much. The ability levels of each of our dc are too far apart to combine comfortably for us. I enjoy having each of our dc doing what it is that seems to fit them best, and I also like having the younger dc finish school earlier than my older ds, as the shorter amounts of times and the shorter length of lessons fits them better and gives them time to just play and be kids.
LHTH only takes abut 20-30 minutes a day to do and is such a wonderful way to start little ones out with homeschooling. It is steeped in God's Word, and centers all around timeless Bible stories read chronologically. What a neat way to introduce little ones to living books!

The fingerplays, letter sounds and activities, etc. teach needed beginning skills while keeping school fun and doable. I think your dd would enjoy the older Bible option of "The New Bible in Pictures for Little Eyes"; the other Bible may be too young for her. You could choose either devotional - they are both excellent. We have enjoyed "Big Thoughts for Little People", but then we are partial to anything Kenneth Taylor authors.

We are currently doing LHTH for the third time with our third son and still loving it.
Beyond only takes about 2 1/2 hours to complete. It is a heart-stirring way to teach American history. The books are very narrative, and the way the Lord is woven into it all within the HOD guide is memorable. CM skills are taught in such a way that dc can truly feel successful with them. The oral narration guidance was especially helpful to our dc and has helped my older 2 dc to love oral narration and to thrive with it. We also enjoyed the copywork of classical poetry and the lessons that accompanied them. All of my sons enjoy poetry, and I know it's because of the manner in which it is done within HOD, which of course took CM's lead on this.

The spelling lessons were an excellent stepping stone for the dictation to follow in the next guides as well. The Bible study gave us some heartfelt discussions, helped my dc memorize some good Bible verses, and taught my dc the habit of seeking the Bible when in need of direction. We've done Beyond twice and found it to be a delightful program to teach. Bigger Hearts as a follow-up to Beyond finishes out American history with a biographical slant that is very living and full of American heroes to appreciate.
Doing 2 (or even 3) HOD programs, especially when one of them is LHTH, is not hard to do, but instead a very enjoyable way to spend our days homeschooling. I think you are well on your way to fine tuning an excellent plan for your dc. Please don't hesitate to ask more questions, as we love to help one another here on the HOD Board.
In Christ,
Julie