Tracey,
My older one usually work independently and at their own level even if more than one is usuaing the same materials. We did have 2 in the same math, but they didn't do it together. They just don't like to work together LOL. For the younger ones I do teach in groups for a few thigns like writing, latin, bible, history and vocab. My 7th and 6th graders are both in Saxon 7/6 and I teach that together too.
For scheduling I plan time first thing for my highschoolers and we go over the days work, correct things or explain things they need help with. The younger ones are working independently during this and once I am done with the HSers I just rotate around helping the younger ones as needed. Then we have group time where we do the subjects in a group like latin etc.