On number 2 above:
on an iOS device (iPhone, iPad) make sure you have automatically connect disbaled
Then, put your device in Airplane mode (turns off cell service)
Then go to the wifi setting and select the MTH unit. It should ask you something like "xxx is not connected to the internet" and if you want to proceed. Say yes
This will prevent your device for jumping to a router that has an internet connection
I put my devices in airplane mode as I don't want anything to disrupt my connection to the train stuff. Same thing on stage, always airplane mode when connected to the FOH or monitor desk.