Ultimately, "direct supervision" can only be accomplished two ways... one-on-one, or tie 'em together. Use Gordian knots!Although other dives in the Advanced class may be executed otherwise, the PADI standards state that the Deep dive MUST be done under "direct supervision". This means the instructor or a CA must be able to see the student throughout the dive. Allowing a student to descend in any other way is a standards violation...
All other arrangements leave "direct supervision" at the discretion of the supervised.
Rick