I know this is extremely late, and the show probably already happened, but I wanted to add to the discussion.
In university we did 2 separate shows with hangings. I was involved in them, but not directly with the rigging. But the way it worked was the actors had harnesses that went down their legs and around their feet, they were clipped into a line that went up to the grid, and was rigged safely. The rope followed the line from the grid, and the actual noose part was a tube that had rope wrapped around it to look like the knot and the end of the rope was pressure fit into the tube, so if something happened they would just fall the two foot fall to the floor, and the noose would come undone.
I don't know if there were any professional companies called in to help, but I believe the carp professor was a certified rigger. The actors were weighed by the carp professor before the concept was put into action, and was weighed again as they were setting up (a few weeks later) in their full costumes.
Obviously, no matter what you need someone certified to come in and help you guys. But there are ways to do it.