You need at least two Setups for multi-spindle turning, one Setup for the main spindle and a second Setup for the sub-spindle. The Z axes of the two Setups must point in opposite directions.
The origin of the two setups can be positioned at any convenient point on the part.
Features are associated with the current Setup. For multiple turret cutting, the Setup associated with the feature dictates which spindle holds the part while the feature is being cut. The Part View displays a list of the Setups in the model, with the Features on each Setup listed below the Setup name.
The part must be moved between the two spindles using a collection sub-spindle features and perhaps bar feed features.
Machine simulation shows each Setup cut twice if there is a sub-spindle move.