Once you have the key, head down to the prison area ( 29, -132, 262 ) /waypoint 29.28, -131.75, 262.49 and unlock the cell with the 2 Reet prisoners.
Use the Reet Marching Orders on them and they will follow you, one at a time, to the area where the water spout is ( -29, -132, 144 ) /waypoint -29.10, -131.86, 144.39. Please note if you have your character set to auto ranged attack you will attack the slave before you can cast. Therefore change to forced melee and stand back.
Note: You must have the Reet Marching Orders item equipped in your charm slot for it to work.