Both of these include project seem to operate in a similar fashion. they are both slaves waiting for pin change on two pins.
The wiegand implementation you currently use does not use the pin change interrupt but the hardware interrupt pins D2 and D3.
With only 3 x pin change interrupt vectors they would need to be time shared. (Time division multiplexed)
I don't see why you need to have a time sharing or time division multiplexing here. You can have both functionality implemented, you just have to make sure that the interrupt routines are as short as possible, moving all time consuming stuff to the loop() function.