I still have questions... (Spoilers)

I really enjoyed the movie, but I did have a few unresolved issues.

1. What really did happen to Claire?

2. If you're so focused on getting over your grief, why kill everyone? (I know it's a cult, but what purpose does a mass murder/suicide serve if they're unknowingly participating?)

3. How did none of them know that was their end game??? After showing the video, Eden and David really drive home the point that death isn't something they have to go through alone and they don't need to be scared. In the video that woman died with people around her then the hosts start trying to convince everyone that death isn't really scary? I'm with Claire, I would have left.

4. How were there police sirens if no one had service? I know there were other red lanterns signifying their participation, but supposedly no one got service there. It's 2016, who really has a landline these days? This one isn't a big deal, just wondered.