As Ed and I mentioned, you probably need to do some investigation on how the different buttons and/or other parts of the XBox One (or other) controller are wired,
if you wish for the Teens to stimulate the press.
There are several different ways that some of these buttons and controls might be wired.
Example:
simple buttons. Where one side of the buttons are tied to either GND or some voltage, lets say Vin. The other side is typically pulled to the opposite side through either a Pull UP or Pull down resistor, which could be built into an internal processor or through an external Resistor. Note: I am assuming Normally OPen type button here. (Only makes contact between the two sides when pressed). So, for example, if the button has GND on one side and a PU on the side the at connects up to the IO pin, then when the button is not pressed, it will logically read high. when pressed it will short out the signal, so it will read LOW... Probably easy to emulate, by adding Teensy IO pin to the signal side and pull it low when you wish to emulate a button press.
Obviously opposite if button has +vcc on the one side and a Pull-down resistor on the signal side.
But maybe they use a button matrix instead. Guessing not, but for that you would need to setup IO lines on both sets of the IO pins. and figure out what they are doing.
For example with a 4x4 matrix, you use 8 pins to be able to read in 16 buttons.
Or again maybe not likely, maybe they used some form of resistor divider type circuit, to read in through an analog pin, the state of multiple buttons. I have used this before, a long
time ago, on my own remote..
Then some of their buttons, are not just simple on/off, but are probably analog. This includes the actual joysticks as well as the RT and LT buttons.
These may be harder to emulate, without using something like an external DAC (Digital to Analog converter).
Then there are probably things like Gyros and ...