this might be more simpler than what you are looking for but try putting down 6 different triggers, all for one individual group. To make triggers for a group:
1)create trigger
2)press F2 (or click on groups), and drag a line from the trigger to the group. (group the trigger with the leader of the squad basicly)
3)double click on the trigger you just grouped, and where it should normally say 'west, east, resistance, civilian, all, none' there should be the options of 'vehicle, whole group, group leader, anyone from the group'. Select anyone from the group from that list.
4)Repeat six times for each trigger (a trigger per squad).
if you want only one of the triggers to trigger and the rest not to, then for each one:
1)in the 'on activation' field put : trigdone = true
2)in the 'condition' field put : this and not(trigdone)
make sure you also create a trigger which executes right at the mission start and defines trigdone = false
hope it helps, 'syntaxes not guarenteed' as some say