I am working with 5 children this year (15, 13, 11, 8, and 6) The oldest is doing her own thing(except for Latin and Pilgrims Progress Study that she is doing with the 13yo and me). I combine character building, SOTW, some read alouds, some memory work, composer and artist studies for the rest. I combine the 3 youngest for Science and Geography. Then they each have their own Bible work, American history, language arts, math, and nature readers. So far so good :) (we are just finishing week 4) The other thing is that I work with the 3 youngest 4 days, the 5th day is a very light independent day. I work with the 13yo 2 days keeping an eye and checking to make sure things are going well and then on Friday(the day I don't work with the youngers), I concentrate on the 13 and 15yo for the day. I have really enjoyed this time with my big girls, we have been having such a great time :)
Another thing that has been awesome is that we save game time (Wii, Playstation.....) for Fridays after all work is complete. This has been one of THE best things I have done in a long time. They look forward to this and I actually get SOME peace and quiet time during the weekend!! We make Friday a day to look forward to to kick off the weekend. They get to play games, watch some movies, have a cup of soda, and they have a slumber party in the living room.
Now that I can see that this is working, I am using this weekend for some more fine tuning to make things run even smoother. I need to have everything planned out or it just doesn't get done. I have been at this long enough to know to adjust as we go to make things work for us, but I need that blueprint to make adjustments from. I have not found an all in one, laid out program that suits us. I know what I want for my kids and what we like and I just fill in the blanks.
HOD does look like a great program and I did try it at one point. I could not get it to work for us.(I am stubborn :) I have my own ideas of what I want and between cutting what didn't feel right for us and trying to combine where I could it just made it more crazy and complicated!) But if you can just follow the plan and go from person to person all day it might work for you and your family. If I only had 2 or 3 children, HOD would be in the running for a program that I would consider. Again I am sure it is a personality thing, you need to know yourself and your children and be honest about your needs and desires. Then there is that dirty word (said in a whisper ;) ) money, oh my!
ETA: I think SOTW and Apologia are great choices to combine your 3rd and 5th graders!