Solution
If you want to use two separate joysticks, you will need to add another joystick reference in the begin VI and read from the second reference in teleop VI as the second input into the tank drive VI. An example of the begin VI and the teleop VI implementing this can be seen below:
Figure 1: Begin VI where we add an additional USB joystick
Figure 2: The addition of our second joystick, where we index out the needed axis for each and send it to our tank drive