You have to ask the instructor. Who knows what the purpose of the drill was? Its a drill not a match.
There are lots of right answers depending on the purpose of the drill
- Both crash net
- One crashes net one takes position around the service line
- One approaches the other stays back (less useful) but comes in eventually as the point is played out
- Any of the above yet determined by the placement and quality of the approach shot (which would be a useful doubles concept to practice)
Its weird that the instructor didn't discuss the purpose and doubles principles you were to work on in this drill