Yes. Model 12’s monitoring is kind of complex, but it is flexible and designed to allow you to toggle between monitoring main bus, aux busses. Each headphone out has a button that determines which bus feeds the phones (up = main, down = aux).
So if you want to listen to channels 1&2 on headphone 1, and 1&3 on headphone 2, you would assign channel 1 to both main (button+fader) and aux 1 (via knob). Then assign channel 2 to main only, and channel 3 to aux only.