Hi,
EAP-GTC is selectable on Android Devices as an option when you configure the SSID. On IOS you don't need to select anything.
However, i had similar cases deployed and it is a big head-ache for EAP-GTC rollout, on Windows. Some of the WiFi adapters were not capable of supporting this plug in and they couldn't connect to the SSID at all.
Its something i had very bad experience on the customer side perspective.
Instead, i installed Windows Server NPS feature and use it as RADIUS Authentication, without EAP-GTC. It is less headache and better user-experience, especially for Windows devices.