Well, I think that the level is easy. Most of the things are done by Elvis XD. But I have to say that even being easy, it's harder than what it looks, at least for me... I had good luck at many places:
- Nice Elvis in first 2 rooms.
- I got those mines (sometimes I don't...).
- A wall in front of me when a guard shoted.
- Good luck on shoting to mini-skedars with Far-Sight.
- Elvis saved me in the Mr Blondes' room.
- Elvis saved me in the end, too.
- ...
In overall, nice Elvis

.
And now, answering your question:
In that last corridor there are 5 guards. 2 of them are 2 stupid invisible guys that appear when objective 1 completes. That's why I throw a mine in about minute 4, not sure. But the other 3 are... Well, they appear when you open that door in the end, not before... Plus, 1 mine doesn't kill any of them... That's why I did throw 2 mines in the end (and even that way there was a survivor...). If you shot all 3 mines at the beggining it happens that the first one makes the others explode, so they are useless, since those 3 guards aren't there still.
Well, hope that makes sense. Sorry for my bad English.