Early Modern book switch question

I have a question regarding switching out books in the Early Modern guide. I know it is flexible and typically is not a problem. However, I have a child going into 9th that is not a particularly strong reader and a very poor narrator. I really want to continue CM methods as best I can, but I think he needs more leading type questions and easier text. I also have a 7th grader so my intent was to read aloud the 7-9th selections. I also have a 4th grader who still loves picture books. So I was also going to include the 1-3rd selections. My question is if it makes sense to have my 9th grader read Notgrass American History over this year and next, rather than America the Last Best Hope. I think the text is simpler for him to read and grasp, and he wont be reading the other selections on his own this year. And also can I swap Story of the World for Stories of the Nations. The kids really like SOTW. Or would all this swapping just mean I should forget the SCM guide altogether. This whole high school thing is really throwing me…..