Hi, what a good news update! I'm glad your father is feeling good mentally too, which is just as important.
Thankfully I am not profoundly deaf, although there are some interesting parallels to your story.
I have moderate/severe hearing loss, worst is 85dB both ears and with tinnitus in both ears. Although I usually hear reasonably well wearing high-end hearing aids and lipreading, I also have ADHD.
Having these two conditions I struggle to manage highest stress-points in life without something going wrong...or mental paralysis sets in - accompanied by louder tinnitus - and my response can be withdrawal within myself.
Long-story-short, my wife joined me at all consultant appointments anyway but soon become my registered carer in order for docs to share my patient info so that she could 'translate' for me many vital pieces of info that I was mishearing or misinterpreting. I can never thank her enough for that.
Since then I often wonder if many (possibly most?) newly-diagnosed cancer patients experience similar to some extent. When all the 'new reality' of their dx starts to sink in patients can struggle to think straight and even with normal hearing can be distracted to the point of mishearing/ misinterpreting what is said.
The 'communications' aspect can almost inevitably make life as exhausting and stressful for nearest and dearest, if not more so than the patient. Not sure there's any easy answers, but support is out there especially if your local prostate cancer group is set up with properly listening ears for spouses/ partners [sadly, mine isn't].
Best of luck with the journey still to go, with hopefully an improved outcome for your father after more treatment.