I'm not good in scripting, and I think this will make a NPC with waitingroom, slot 10 (-1), when 5th player joined, it will triggers the label to warp 5 players that joined.
prontera,155,165,5 script W4iT1n9 R0oM 123,{
end;
OnHmm:
warpwaitingpc "niflheim",0,0,5;
end;
OnInit:
waitingroom "W4iT1n9 R0oM",10,strnpcinfo(3)+"::OnHmm",5;
end;
}