I followed the guide for multiple faces: duplicated the head binding and adjusted the face index. Objects appear in correct location but the blendshape and eye positions for the second face are taken from the first face -> both 3D objects open the mouth at the same time.
How to recreate: Open Template "Face Expressions", select "Pair Open Mouth" animation in preview, duplicate the "Head Binding" and set face index of copy to 1. Result: Both faces blink and open/close mouth at same time as the first person. If you disable the "Character Expressions [REPLACE ME]" and enable "Face Mesh Expressions [REPLACE ME]" it's better visible with the face mesh with transparent mouth/eyes.
I thought the scripts use the sourceObject from the face they're attached to. Or am I doing something wrong?