If on PT Pro I have layered instrument with 2 layers (Piano 1. Piano 2), in which the lower half of the keyboard is played by piano 1 and the right half by piano 2 (i.e. the right half in piano 1 is turned down and the left half in Piano 2 is in note edit/volume), what about symphatetic resonance?
Is there any resonance between the layers, or rather each has its own, and unfortunately it is limited to the keys with volume not turned down?

yes it works correctly, there is resonance between the two layers. (PT Standard)