Guest WiFi - are devices isolated from each otther?

Hello ! You can config this in Luci

http://192.168.8.1/cgi-bin/luci/admin/network/wireless (if your network is 192.168.8.1)

Then Select your Guest Wifi networks there and go to Advanced Settings then down Interface Coinfiguration

Select Isolate Clients

I hope that what is you wanted.