You may enable Client Isolation for a WiFi network so that the clients that are associated with the same or different WiFi networks cannot communicate with each other but still have internet access. As reference, kindly read pages 51-52 of the WAC505 user manual here about Enable or Disable Client Isolation for a WiFi network.
It seems there is no option for Client Isolation in NETGEAR Insight. I suggest you to access the web-GUI of the WAC505 then enable Client Isolation then reconnect the WAC505 to Insight.
