have you considered the bju online content? we've used it for several years and it works really good. you could combine the boys for sciences and perhaps even histories. Plus, foreign language is free when you do a grade kit. I like this bc it frees them up to set their own schedule, it gets them being accountable to someone (the bju lesson plans) other than you, and in the end can actually free them up to pursue more social things outside of their studies.