Also, there is some media that helps. The movie Waking Life is an interesting and comforting view of things: we will, most of us, have a few minutes of brain activity left after our heart stops. Waking Life‘s take is that those few minutes are…sublime.
The philosopher Plato wrote his stuff in dialogue form, using Socrates as the primary interlocutor. Remember how Socrates died? (in real life) – he voluntarily drank poison rather than flee Athens. When his friends tried to talk him into another course of action, he refused, and argued that the soul, as something essentially alive, can never be dead. Now, I personally tend to follow the same theory that your unfortunate relative ascribes to – that we end, and that’s that. However, this dialogue of Plato’s almost had me convinced otherwise, the first time I read it. Not that I think you ought to use it to try to change his/her ideas on the possibility of life after death – it’s that Plato’s argument makes a good deal of logical sense, and is simply comforting. Here is a full, free copy of this dialogue. It’s named the Phaedo.
Finally, there is the song Don’t Fear the Reaper by Blue Oyster Cult, and Dust in the Wind by Kansas. Back when I thought I was going to die soon, I used to listen to these songs quite a lot. They helped, partly by giving a window to other peoples’ feelings about dying. And Dust in the Wind let me grieve for myself without being self-conscious about it.
In general, I would tend to say that reading and listening to other peoples’ descriptions of death is what best helps to prepare for it. Which is also why I think a group makes sense. Imagining oneself in another’s place, who has been there before, is a good way to mentally “practice” for whatever place that is, which you yourself will soon be inhabiting. Of course, death is a special case, because no one can really tell us about the experience – and it can’t rightly be called a habitation of any sort. But speaking with a group of other people near death, and taking in certain media such as those I mentioned above, can get us closer.