To set up the ailerons on two different channels, you only need to activate the flaperon mix. Just set the flap movement to zero if you don't want flaps.

For two elevator servos on different channels, use the Ailevator function. If you don't want the elevators to work with the ailerons, then set the aileron amount to zero on that mixer.

You don't need to use Pmixes to get this job done.

Just follow the manual for such a setup. It's not complex at all.