What tense is appropriate when a group includes alive and dead people?

In a recent article, I was comparing the atheism of Joseph Stalin, Ayn Rand, and Christopher Hitchens. Which of the following sentences would have been appropriate to describe them?

1. All three believe that there is no deity.
2. All three believed that there is no deity.
3. All three would agree that there is no deity.
4. All three would have agreed that there is no deity.

I would go with #4:

All three would have agreed that there is no deity.

This kind of conditional is the only satisfactory way to group together the beliefs of the living and the dead.

None of the above. Most of the time, the best option is probably to choose one, use it consistently, and trust your readers to have a smidgen of sense. If you feel that you have to be crystal clear, then you need to be specific:

All three believe (or believed, in the cases of Stalin and Rand, who are dead) that there is no deity.

or

All three believed (or believe, in the case of Hitchens, who remains alive) that there is no deity.

It's better to go with the present tense since a person's influence reaches beyond the grave, but it's unflattering to speak of a living person as though they're dead.

With due regard to @Robusto's answer (which I don't totally disagree with), @palooka's comment thereon, and @Caleb's unassailable assertion that strictly speaking you can't use a single tense for past and ongoing actions simultaneously...

If you have to choose the best of these four, go for the third.

• 3 All three would agree that there is no deity.

The conditional "would" implies they'd only agree on this matter if they were asked. It's of no great consequence that in practice we can't retrospectively ask the dead ones. The whole statement is phrased as a conditional anyway, so it's all hypothetical, and needn't happen/have happened at all.

I'd be inclined to think this very sentence illustrates how casually we ignore the implications of the conditional tense in some constructions. The 'd there stands for "would", but I imagine many people hardly noticed it. Obviously I must have meant "am", not "would be". By the same token, we don't notice the conditional in OP's example - we just assume some kind of "present" tense.