I've vaguely understood what you need, but not very clear on what exactly you are planning to achieve. What exactly is allowed/not allowed in this presentation of yours, and what do you have to do or not do to get blacked out or not? What is your PA going to exactly do, and what is the communication objective? How much do you want to spend?
If discretion without observation is important, you could do with a wireless lapel mic and a receiver. That solution is pretty expensive. The option at the other end of the price (and usability) is an FM microphone with an FM radio at the other. If two-way communication is required, then it's a different ball of wax.
Then there's Bluetooth, and two headsets plus a single laptop with a single dongle should be able to sync up. If you have an internet connection or two and two laptops with built-in mics, all you need are two pairs of earbuds.
There's four ideas up there, take your pick. I have no clue what is possible or not among all of the above, it's down to what the exact situation and resources are. Hands-free units connected to cell phones will generate interference, but I suspect you have no microphones at all, going by your description of the venue.
If it is just prompts, then there's nothing to beat a little FM radio tucked out of sight, and a FM microphone for your PA.