Hello all. just letting you all know that you can use the suicide method and still get this achievement. With 6 players just have it be 1 vs 5 and the 1 fella can kill themselves over and over.
This way you can use any map. It will take a little longer than just using the Killhouse method and just killing the leader but, if you are all to lazy to kill, then just use this method.
Remember to help the last person get the achievement