
I'm glad to hear that his health is improving. That's the important thing!
On the hearing, our daughter who has Autism, heard selective sounds. For instance, when she was about 2 1/2 years old I tested her hearing by getting up behind her while Momma was playing with her and looking at her face. I banged a stockpot and its lid together rather loudly, and my wife said she didn't even bat an eyelid. My daughter just kept on playing as before. Then I walked upstairs in the townhouse and quietly whispered her name. She immediately dropped what she was doing, looked up the stairs, and came and found me.
So because of these things we had to learn sign language to teach her words like "more", "sit", and "all done". She caught on very quickly!
In college, years before, I had done a graduation paper on "Learning Styles and Teaching Strategies". I learned in that paper that all people and cultures (who can see - not blind) learn language by referencing objects to associations such as other objects ... kind of like an orange and a beach ball are both spheres. Those are concrete references. Letters and phonetic sounds are very abstract and difficult within communication to adopt (thus schooling is required). Sign language is a happy medium because though it is abstract it is familiar and it is an easier bridge to mentally cross better so than interpreting either spoken or written language.
We were fortunate, in that, we found that changing our diet a bit helped with our daughter having more of a relaxed mind. Her hearing had to do with how her mind processed sound rather than her actual hearing. She passed her hearing tests in the doctor's offices just fine since they were testing with sound waves rather than speech.
Now are daughter does very well, and we don't use sign language much at all unless we are in a quiet setting that requires it. I am pretty sure we are going to teach all of our soon-to-be-coming triplets sign language since trying to talk over all three of them plus our other two I am envisioning to be a nightmare.