To come back at that how many people you need to be kicked discussion, me and a friend (me blm and he whm) did keeper of the lake once.
The tank and dragoon were friends aswell, and after a wipe or 2 on the last boss where the dragoon got hit by almost all the aoe (how original for a dragoon) and my friend could barely hold up all the healing with ressing him 2 times, without any reason i just got kicked after it, while i was the only dps alive and only got hit like twice max. My friend chose to leave aswell, because he couldn't make it trough with a dps like that guy.
So yeah, 2 friends in one dungeon can be quite unfair if they decide to kick someone >.<