The Cabin at the End of the World
That's the title of the novel. You can google it to find out more. People who believe in an apocalypse are usually psycho.
Wikipedia plot:
A gay couple named Andrew and Eric and their adopted daughter, Wen, are taking a vacation in a secluded cabin in New Hampshire. Their dwelling is invaded by four strangers named Redmond, Leonard, Sabrina, and Adriane who take the family captive and tell them that, to prevent the upcoming apocalypse, one of them must be killed by the others.