Yes, A "Y" harness is needed to use 2 servos on ailerons.
I've never seen a setup with each aileron on its own channel...

Dont overcomplicate things though. For a .40-.60 size trainer with the forces required to control it, a single servo will suffice IMHO.
Either use torque rods or route a NyRod through the wing to about 1/3 the aileron span and connect using control horns.