Starting question: Is there a way that they can at least broadcast to WIFI from the outdoor PA? That is, do they have WIFI at the PA location?

If so, then they could use something like Chrome-Cast https://store.google.com/product/chromec...CFYcUPwodLuAJbQ

Follow on question; if not, do they have line-of-sight from outdoor PA to a place where they could run a cable into the lobby?

If the answer to that is Yes, then you can use a wireless in-ear monitor system, with the transmitter at the PA, and a belt-pack at the entrance to the lobby. Then from there a wired output from the beltpack receiver to a PA in the lobby.

Finally, if it's a really fancy hotel, they might already have an audio over LAN system built into the hotel's PA system and your son just needs to ask how to get source material onto the network for selection at the lobby.