bluesmokebass has the right answer on this, but I thought I should let you know that you only need to do that quest if you: a) need the caps, b) want to have convenient map markers, or c) want to avoid all negative charma. If these don't apply to you just go find these three and pickpocket their "special key" (you could kill each of them for their keys, but in that case you should definitely do the above quest as you get paid for doing that ;D). P.S. the keys let you get a unique set of power armor.