Tamara gave some good thoughts already - DITHOR is very flexible!

We have done this a few different ways, based on what I felt each of our dc's needs were. The first year Riley began DITHOR, I decided it would be best to just do them separately. Riley really needed DITHOR 5 days a week, and that would have been too much for Wyatt. I liked that very much, as it kept my time and focus more on Riley, and he needed me more then than Wyatt did for DITHOR.
This year, we have done DITHOR together 3 days a week and enjoyed that too. We do it whenever it is scheduled in Wyatt's RevtoRev's plans. That keeps the balance of LA/amount of writing intact for his guide, which I felt was more important that doing for Riley's PHFHG's guide. We do the Kickoff and "All Levels Together" days together always. I read the 4 final project ideas to them at the end of each genre (4 because there is the Godly Character Project, the Group Project, and a Book Projects to Send Home project for each of their different levels). I let them choose, and it's been interesting to see what they pick. They've sometimes chosen to do projects together, sometimes separate, and sometimes Wyatt has done Riley's age of "Book Projects..." and sometimes Riley has done Wyatt's age of "Book Projects...". All have been fun!
As far as the reading out loud and discussion questions go, I usually send Wyatt to read independently first, as he has more to read. I have Riley read 4-5 pages out loud to me and let him finish on his own. I then have Wyatt read 2 pages to me out loud - I feel this is important for him because he struggled with speech early on, and he still sometimes will mispronounce words. Plus, I can easily keep tabs on the storyline this way. Usually Wyatt is still finishing his reading then, and Riley is done, so I ask Riley his discussion questions or give him directions for his Student Workbook. At that point Wyatt is done reading, and I ask him any questions and see if he has any questions about his Student Workbook assignment. Sometimes, when I finish with Riley, Wyatt is already handing in his Student Workbook. Wyatt is in Level 6/7/8, and his workbook directions are written directly to him in his Student Workbook. That is just the way we do it though - the possibilities are endless! I hope this helps!
In Christ,
Julie