A mate of mine had it far worse than me. His dad got it and was very difficult to live with. He became aggressive towards his wife and kids, he used to wandering off and get lost and have to be brought home by the police, who told the family not to let him out, but he was a bit of an escapologist as well! It got to the point where he couldn't look after himself, so his son had to stop working and stay home to care for him, as his mother was too old and frail. The strain it put on everyone else in the family was terrible.
I think it's very good advice that you give about "going along with it" and not contradicting them, especially if they are likely to get upset by it. At first it's hard to do that, because you don't want to see them deteriorating in front of your eyes and sometimes it's easy to feel like responding..."don't be silly, you know that's not the case" or whatever. I remember my mother saying to me, "I've not seen my mother for ages...is she still alive?". Her mother (my Grandmother) had been dead about 30 years at this point! That was a tricky one because if I'd said, "you know she's dead mother, she's been dead years" it could have destroyed her. And if I said, "she's fine, she's still alive" - that would have been a terrible lie and might have raised expectations which couldn't be realised. I can't remember exactly what I said now, but it was something along the lines of..."don't worry about that...tell me what you've been doing today?" In other words, I changed the subject quickly. And the thing is, I found she'd usually be easily distracted by that and then move on to talk about something else. It didn't feel comfortable, but it avoided what might have been a very distressing situation for her.
It's hard to know what's the right thing to do sometimes.