Thank you Carrie for your input! Your sister and the other ladies have done a wonderful job of answering my questions, but it IS nice to get your perspective.
And, for anyone who is wondering, I declared Friday the last day of school!

My kids did both ask, "Can we read more history this summer?" Since we have always done a "living books" type approach to history, I probably won't tell them no, but perhaps we'll just read together instead of calling it history. But they sure do like to read LOTS of books about the same era and topics to get a good picture of what they are studying. They also both asked if they could do math this summer. I told them, "Probably not until August." (I'm a MEAN Mommy! "No you can't do math!") But, in this case, I really think it's best. I WILL be working with DS on his handwriting. He just needs more practice.
As far as the specific curriculum, I am excited about trying Bigger (I think), but I admit, I am a little nervous. The plus side, I have probably 90% of the books for Preparing and about 75% of the books for Bigger, so it fits in nicely with my own pre-planned ideas.
Carrie, I was also wondering if topics like Castles and Knights (Middle Ages stuff) and the Renaissance and Reformation are covered in Preparing or where those would be covered, if not. My kids are REALLY looking forward to those studies!
My DS is going to be in Singapore 3B in the fall. Will that work pretty well with Bigger? Also, he has not done much narrating and no dictation. He has never done R&S English either.
DD is going to be in Singapore 5A and is part way through Grade 4 of R&S English (Building with Diligence). But, I have no trouble just scheduling her math and English (or having her do the next lesson each day). NOT A BIG DEAL.
If we do Bigger when she is in 5th grade, will that work pretty well for getting her "ready for high school"? I know that you haven't even written those books yet. So, it's not a very fair question!
Thanks again for your hard work and the thought and effort you put into all of this. It is evident that you want to glorify God in this work.