Best answer by ratty
Sonos doesn't support Standard Setup on a guest WiFi, and one suspects you could struggle. Guest networks typically don't permit access to the wired router ports, preventing you from changing the Sonos system's stored WiFi credentials in the usual manner (or indeed running in BOOST/SonosNet mode). Moreover many guest WiFis can stop attached devices from actually communicating with each other at all (wireless client isolation), which would clearly block a Sonos system from working entirely. Some routers have a switch to enable/disable such isolation.
In the absence of an option to temporarily wire the system, you'd need to factory reset everything and start from scratch. Before doing anything more I recommend you move a controlling device onto the guest network, factory reset just ONE Sonos unit and see whether you can set that up on the guest WiFi as a new system. If the controller fails to find the player you're scuppered. Assuming you have multiple Sonos units you can at least add that player back to the rest of the system, restoring things to the way they were before.
What's the reason for not handing over the WiFi password anyway? Presumably as a vacation property there's precious little in the way of network resources (NAS etc) that you'd be concerned about?