Thanks for your response. Lots of good things to consider.
Cost is definitely a factor, but having them work together and be able to have discussions together is important, too. My oldest ds is an introvert who has been homeschooled since K, until last year when he went to a Christian school. He would like to return, but a job change has made that impossible. He is also in the habit of speed reading through everything and completing assignments rather than lingering and going deep. My middle ds reads more slowly, thus deeply, and considers questions beyond the assignment. So ideally, I would love for them to be in the same level for dialectic discussion purposes.
Also, ds1 desires to complete work in a timely way, but has some very real executive function issues that can make this a challenge. By having them work together, there is more accountability and structure (ok, and competition because who wants to be 'shown up' by little brother?

)which helps the executive function issues tremendously. Of course, I'd like to join in on some of those discussions.
Finally, we are doing some outsourcing for ds1. He has surpassed my ability to teach him English/Grammar/Writing because he is much better than me at this point, so he will be taking an online Lit based class for this. I have also enrolled them both in a budget friendly Spanish class in the community, more for the social interaction (they've both had 2 years of Latin and we'll be continuing Latin at home, so expect Spanish to come easily) and in a chemistry lab for homeschoolers offered by a local Christian school (with the idea of doing Chem/Phys in WG with ds2). And he will be finishing up his current math with TT before moving on to perhaps ChalkDust Pre-Calc (if I can find it used for a reasonable price!) So he really just needs History and Bible, which I would love to combine with his brother, so a full guide for him is really not cost effective for us currently. Sorry to not make all that clear from the start! It's an eclectic kind of year for him!
It seems the thinking your response made me do has made the core of my dilemma a bit clearer for me. Thank you! I have loved HOD since I first used it in 2010, but we only used it for one year before being unmistakably called into Classical Conversations. We have now been unmistakably called OUT of CC and are just trying to put the pieces together. Since no two programs really 'mesh' very fluidly at the HS level, this is a bit of a challenge. We're down to HOD and Sonlight to figure out the History component, so will continue to try to figure those out!
Thanks again for your wise words!!