You could use the unit collision type like in mazes:
In the Events you will find
Unit- unit within range ---Then you set it something like this:
Unit - A unit comes within 50.00 of Demon Hunter 0012 <gen>
50 is how far away, you should test this before you really do anything else
When it asks you to pick a unit, just click on your unit that you control.
Then for actions:
Unit - Issue order targeting a point ---it will look like this:
Unit - Order Demon Hunter 0012 <gen> to Move To (Center of Region 000 <gen>)
(THIS WILL MAKE THE UNIT WALK TO POINT)
If you want them moved instantly:
Unit - Move unit instantly ---will look like this:
Unit - Move Demon Hunter 0012 <gen> instantly to (Center of Region 000 <gen>)
For these, of course you will have to do 2 seperate actions for the 2 beings going to the arena.
Hope that helps, let me know if you need help with it.