Chevis, totally agree on the story telling angle.
My advice is to break up the lecture the part. Keep alternating between lecture, demo, practice. This keeps everyone on their toes the entire time.
For example, you could do a short 10 minute intro and a bit on psychology of the sketch. Then do a very simple exercises, like drawing a smily face vs drawing a sad face. Have everyone do it, then talk about how much complexity of concept they just achieved. I try to break everything down as simple as possible… i.e. draw a crowd, a bunch of circles with the front row having smily faces… showing action, arrows in space… that kinds of stuff. Do that 3-4 times then have a brief wrap up convo and boom, 2 hours gone.
I think you are on the right track with a focus on communication of concepts and ideas vs quality of sketch for this mixed group.