How many people do I need to kill these three mobs?

[Atmas]

If you can break into hate and are clearing it you shouldn't have any problem with Thought Destroyer.

The Keeper of the tombs is like a 5-7 day respawn which sucks. Not many people need him but it seems like he gets killed a decent amount. Probably a one group force.

Kirak Vil should be one groupable as well and I believe still frequently up.

True Miragul once again, a good group of 55-60s should be able to do.