guest subnet with more than 1 member

Currently, every device that connects to the guest network is assigned a different subnet, which is great for isolating guests while giving them internet access.

For my primary WLAN i prefer to use WPA2 and a 48 or greater character random alphanumeric passcode. However, some products have issues with that. For example, i use a meteobridge device to publish weather data, but it will only allow a short passcode. I currently have it using the guest SSID, but then the associated webcam can't talk to its bridge. Ideally, it would be nice to assign a group of devices to share a segregated segment so they can see each other but be isolated from the primary network.