I'm looking for a book trilogy/saga/series (NOT a standalone) in which a group of people are cut off from the world and each of them starts dying.

There are 2 variants to this:

1) A game with all the people competing with a battle to the death. With rules and all.

2) Each of them must unmask a killer with every character having dark secrets, and/or a dark agenda.

In short, battle royale and/or an island with liars style. This is very important to me, so any help is appreciated. Thank you in advance.