Why are Isabela and William in the restaurant?

Could someone please enlighten me as to why Isabela and William are in the same restaurant as the minister, the captain, and the sergeant? It would be an unlikely coincidence. Is it because William wants to attempt to listen in on "the sinners'" conversation? Or what? There's probably an explanation, but I just can't figure it out.

Actually, it would be great if someone would take me through the explanation of the events leading up to the characters' situation step by step, in detail. (Spoilers galore!) I understand the basics, but it's still kinda dim to me. Maybe watching it again would help, but I just can't bring myself to do it, because it's SO long-winded, while the flashbacks are mostly extremely quick and confusing (to me).

Was Isaac the foreign minister? What was the connection between Isabela and Isaac and his wife? Was she his secretary? It's pretty much all a blur to me by now, a day after watching the film.

I read a discussion post in which someone said that the reporter, William, was in the process of uncovering the 'conspiracy', but I've forgotten (or not noticed) how that was shown in the film...?

On a different note: Someone (Dyer's character?) says that it wasn't Chloë's time yet. But it WAS both Isabela's and William's time? And the waiter's? (And more? Were there more people in the restaurant? Sorry, I don't remember.) Doesn't that seem strange somehow? And why, incidentally, isn't the waiter (and others?) around after the bomb, along with the others?

One more thing: If the characters' situation is purgatory, and they're trapped in repetition, then how are they supposed to learn from that repetition if they have to start from scratch every time, remembering nothing? Are we to believe that their memory will be a bit clearer each time they go through it all?

Hmmmm, maybe I shouldn't watch films that require a brain. :D

Help?