There would be switches involved and a lot of locations
Here are my ideas:
For teh randomization, make like 4 locations, each named a something like 'A' to 'D'. Now, go to the triggers menu and make a Condition: 'Command Atmost 0 Unit', 'Switch 1 is Set', 'Bring Unit to Pick Hero'; Trigger: 'Create Hero at A' and so on.
But for the randominzation (sorry), make a Condition: 'Always', 'Randomize Switch 1' and so on for the other four switches, and 'Preserve Trigger'.
And the spawning of the Heroes, you've probably already got that figured out:
Bring unit to Location
Switch is Set
CreateUnit At Location
RemoveUnitAtLocation
I hope that helps.