It's even worse that they knew all the trouble everyone went through and still weren't considerate enough. Truly self-centered and just plain mean. Your sister and BiL can't be the only ones who'd already bought tickets, right? If anything, they should have their own party and not invite the causers of stupidity.

I'm glad they've got a full trip planned out and are taking advantage of a not so good situation. Have no fear, everything will work out for them. I know there's a bit of fear, but they know what to expect, right? And they would also know what to do in case of any event, so they are going in prepared. It'll be fine. I'll even keep my fingers crossed. :O)