It sounds like you’re on the right track, Amanda. Great idea to have the 13yo follow along in his Bible!
Are you able to spread out the readings throughout the day, interspersing them with other subjects? If you can do that, it will give your voice and your mind a little break. (And Charlotte said that sometimes a change is as good as a rest. 🙂 ) I realize, though, that with special needs kids, sometimes they need to get all the reading done at once. So do what works best for your situation.
One other suggestion: if you are feeling overburdened right now, you could take a break from reading artist and composer bios if you want to. You could just do a picture study once a week and play the selected composer’s music in the background during lunch or something during the week. You could easily add bios back in as you are able later, but feel free to simply introduce the children to the artist or composer’s work and get out of the way for the time being (and give yourself a break at the same time).