In the decoder line up proposed from Rokuhan there appear to be both mobile and stationary decoders, going by photos from recent Jam train show in Tokyo.
WiFi you have to download the app to your device android or other so it your device does not have a chip it is not a smart phone, so internet etc. is not from a telephone network but via WiFi to household modem.
The E-train controller has two track feeds if you are using their plug in system, you can control two loops of independent track, you can see that in their video for dc operation, and with your tablet in landscape mode you can have two throttles on screen at the same time, each controlling a separate engine. In DCC mode you just need one track feed to control multiple engines. As far as tablet to controller only a single pairing is possible according to the documentation.