As long as you’re careful about not having 5Ghz frequency channels overstepping their frequency you won’t have any problem.
I’m running 4 or 5 headsets on a single wifi router, currently happy with 12 headsets divided on 3×5Ghz wifi with channels that are clearly divided on the 80 Mhz bandwith
As long as the router wifi is 5Ghz , with a good quality (headsets are 5 meters from the routers) No trouble at all with a 50Mbps video stream in virtual desktop with a stable latency around 35-45ms.
Tested with multiple wifi routers. Cheap huawei or expensive Asus ROG wifi routers. All having the same success and no visible difference (a few more ms in latency sometime with the cheapers models)
I think 18 headsets would be doable depending on your location and if you can install the routers in a “smart/central” position. I did 16 headsets (Oculus Quest 2) with no trouble, 4 wifi routeurs behind a 5 years old basic 1Go RJ45 netgear switch
You just have to be carefull of customers using their phones as hotpots as it can f**k everything up (monitor your place with a wifi analyser on the 5Ghz)