I don't have much to add, but I do want to express my support. You and your entire family will be in my thoughts and prayers.
My grandpa (mom's dad) had Alzheimer's and lost a lot of his communication skills in the last year and half before he died. The last year before he died he had a massive stroke that we thought was going to be fatal. He was in the hospital for almost a month and we waited for the call almost everyday. He lived for just 2 weeks shy of a year with a feeding tube, but had pretty much no quality of life.
Anyway, sorry to digress, I think touch is a big thing. Grandpa always smiled when we hugged/kissed him. Is there anything that Terry's dad enjoyed doing that he can still do? Like throwing a ball or going for walks even if it is in a wheelchair. I think the big thing is that you are there and trying to spend time with him.
Now as I look back on my earlier sentence, I realize it seems like I might be talking about a dog asking about balls or walks, but I ask that b/c my grandpa played on a softball team in the Army during WW II and that was one thing he never lost was throwing and catching a ball. Even up until he had his stroke he was throwing a soft nerf ball at/with my cousin's. And Could HE throw!!!!! If you were in the room and not paying attention he would nail you with it and when you would look at him he would wink. That is how my younger cousin's spent time with him, by throwing a nerf ball. And he could do it for HOURS!!!
Another thing my grandpa was addicted to was candy. He loved Red hots and the pink (pepto bismol - like) lozenges. He would eat those by the handfuls and his eyes always lit up when he opened them Is there a favorite candy that he likes?
The flowers or something that he can ask about is an excellant idea. My grandma had a beanie baby in my grandpa's room. (until it got stolen )
Even up until he had his stroke, and when I would go visit him and they would ask him " Is that Staci" he would nod. He always seem to know me. My mom thinks its b/c I was the one that would "grandpa sit" when he still lived at home. I would go and stay with him if grandma needed to go out for a little while. I helped him to the bathroom and changed his depends (that only happened once I think). Not often, but when I was needed I was there for them.
But I do know that as he started to decline, it was so very hard on my grandma, my mom and my aunt and uncles. He would tell her he wanted to go home when they were already there, or ask where she was when she was there.
I think it would be redundant to say that patience is the key. And as for Terry, I guess just waiting until he is ready to talk about it if ever is the way I would deal with it. But that might not be the right way.