The short answer is that no, AO really isn’t designed to be able to use with the whole family reading the same books. The best way to do it is to have each child in their own, age appropriate, year for history, science, and most literature, and then as Melanie said, combine for things like Shakespeare, artist study, composer study, and things like that.
The books are chosen to be appropriate for the age/grade that they are used with, and it would take quite a bit of modification to combine everyone. So, for example, the year 4 books would be difficult, and have some content not as appropriate for a 6 year old. Year 1 books would not challenge a child ready for year 4. If you have 2 children quite close in age and/or ability, you might be able to combine them into one year, but many people have found even that to be difficult.
I know some people have combined major portions of years 1, 2, and 3, which are the years that your children would most likely need you to be reading most of their books aloud. Then, they separate the students into their own material in year 4, when they are capable of reading many book independently. This would mean that one student might do year 2, 3, and then 1, so the jump to year 4 might be a bit awkward, but it might be possible.
The only other way I’ve heard to combine somewhat is to use one lower level year and one higher level year that deal with the same time period. So, years 2 and 7, years 3 and 8, etc. have similar time periods. The students would be reading different books, but you could have family discussions about similar topics.
