The first person to join a channel is automatically set as the Host. You test this by using:
if(TNManager.isHosting)
{
//Do hosting Stuff
}
If that person leaves the channel, someone else in the channel with become the "Host" and then that IF statement will start working from their client. I quoted "Host" because it's still really just a client. It just has a kind of authority given based on the isHosting being set to true.
Your standalone server is more of a message relayer if that makes sense.