Hi Megan, and welcome to the HOD Board! If you are going to combine, Bigger Hearts is definitely the highest guide I would use with the ages of your dc. I'd be very hesitant to suggest Bigger Hearts as a placement for anyone under 7 yo - it is a meaty program that has quite a bit of writing in it.

Here is an excerpt from a post where Carrie describes the writing in Bigger Hearts...
Bigger requires more writing in the areas of a once a week history notebooking assignment, a once a week science experiment sheet and a once a week science notebooking entry, along with once a week copywork of a Bible verse, 1-3 vocabulary cards each week, cursive handwriting practice daily, and daily grammar instruction with written practice. It also provides a choice of spelling or dictation passages.
I am wondering if Bigger Hearts is a good fit for ds? Technically, your dc are ages 6 and 8 yo, so you could actually combine them in Beyond Little Hearts otherwise, just doing DITHOR to challenge your 8 yo in reading instruction, doing R & S English 2, cursive, and higher level math for her. What do you think? I do think it is possible for the 2 of them to do Bigger Hearts - but I just am throwing out some more details to help see if you think that is a good placement. If ds definitely places in Beyond, I'd probably do Beyond. If ds is on the fence between Beyond and Bigger, you could begin Bigger Hearts slowly - maybe just 4 days a week - and take a little longer to do it, letting ds have time to truly grow into it. You will definitely know best here! I hope something here helps as you ponder placement!
In Christ,
Julie