Uncle Max, you're a very thoughtful and concerned 'occasional caregiver'.
I believe he will grow into his own consciousness in his own time.

How about an outing to a disabled children's home, or an orphanage?

Here are some books that might be fun (yet eye-opening) for him:

"Holes" by Louis Sachar
"The Curious Incident of the Dog in the Night-time" by Mark Haddon
"How I Live Now" by Meg Rosoff

These are 'younger' but a lot of fun:
"Dirty Bertie - Fleas!" by David Roberts & Alan MacDonald
"The Witch's Tears" by Jenny Nimmo