My dad is completely non verbal now and spends much of his day sleeping. He was diagnosed with PD and dementia at the same time six years ago at 75 (very few symptoms ). His rapid decline was helped along by a broken hip which required surgery and we all know the various issues broght on by the anesthesia. ..uggg. Along with being non verbal at this point we are also making a minced diet for him because swallowing is a challenge. I used to think that this was all PD related but in the meantime have learned that it's prevalent in later stage Alzheimer/dementia as well.
Like some of your loved ones here, he was extremely vibrant and a big personality. His withdrawal from friends and conversations were signs of embarrassment for not being able to keep up. We went through a few years where he refused all company. The speech therapist didn't help either and his light began to fade.
During these times I used two things to perk him up and take him somewhere happy.
Old photos. ..I mean very early...pics with my mom from their 20s, me as a baby etc. He loves that. (Unfortunately it makes my mom cry)
Old music from those days is my second weapon to make him smile. (I had to dig deep...music from Germany in the 50s is hard to find...lol)
I found newer pics upset him and reminded him about his decline...old ones seemed to just bring joy. I'm sure most of you have already experimented with some of this...so this long post is really to say "you're not alone" . If you find something that brings them a smile...share it. We all need strategies.
It's a tough road and you're all rockstars!