I have a USB wifi adapter with long range antenna connected to my Raspi which is showing up as wlan1, alongside the built in wlan0 and eth0. I don't understand that if it is possible to offer a local wifi hot spot from eth0 to wlan0 why it isn't possible to exactly the same from wlan1 to wlan0.
Currently I have wlan1 connected to a distant wifi hotspot and I have OSMC setup offering tethering from wlan1 to eth0 and then have a TLink access point plugged into eth0 offering a local wifi hotspot. With this I am able to connect devices to the TLink hotspot and access the Internet connection of the distant hotspot. All the wifi connections are running at 2.4G absolutely fine with no interference.
I just wish I could do away with the TLink AP and just use wlan0 to offer the local hotspot in exactly the same way it would for eth0 to wlan0 tethering.