well, ok, didn't knew you're "noob" (no offence intended)
Here's a how to by using a really short script:
?! (isServer): exit
_dude_array = _this select 0
_my_dude = _dude_array select (floor (random (count _dude_array)))
@ !(alive _my_dude)
"1" ObjStatus "DONE"
exit
This little sqs script you can call from wherever you want...init.sqs would be a good place for.
Name all possible targets (doubles) as you like, i'll take the examples from my first reply:
[[namedunit1, namedunit2, namedunit3, namedunit4]] exec "primary_target.sqs"
you can add as many possible targets as you like to, one of them will be selected as the "true" target and therefor set the objective to "DONE"
Hope this helps
Myke out