Welcome! My DC are of similar ages (13, 11, 9, 6, and 2).
We just started CKE (earth & space) in January. Everyone is really enjoying it so far. I think it’s considered more classical than CM, but I’m finding it to be CM friendly. We are only doing some of the memory work, basically whatever I think may be useful. I split the lesson over 3 days instead of two (one day for reading a living book from the resources listed in the back, one day for reading the lesson, and one day for the experiments). If the lessons are fairly short, we sometimes add another reading from the suggested library books. And of course we add in some narration.
I agree with Karen about math & English. We combine some things like math drills or flashcards (each working on their own type of facts). I also just picked up a book called Bedtime Math that has a short story, followed by 3 different math questions, one for each age group. We’ve been doing these before their math lesson and they only take a few minutes. However, I don’t see how you can combine your DC in the long run. I did manage to combine two of my DC when they were both learning multiplication facts. I split them back up when it was time for multiple digit multiplication so they could go at their own paces. We use MUS, so I generally spend very little time actually teaching. They watch the videos and come to me when they need help. I think it’s very friendly for larger families.
For language arts, we usually do copywork at the same time (each child with their own passage going at their own rate). They also study their Spelling Wisdom passage at the same time, and my younger DC work on phonics at this time. Two of my DC often diagram sentences together. They take turns, watching and learning from the other child’s sentences. We’ve used a couple writing programs as a group: Write On and Igniting Your Writing. Both are geared toward upper elementary/middle school grades.
Have you looking into Winston Grammar or Our Mother Tongue? Both can be used for grades 4 and up. There are probably other options in addition to these two.
Basically, I’ve found it fairly easy to combine two DC with some 3Rs subjects, but 3 or more gets to be a stretch (for the age gaps I have anyway).