A No, not entirely; and, it depends. To clarify, on Dive Four, the instructor must:
1) oversee the planning,
2) conduct the dive briefing,
3) directly supervise the free descent without visual reference skill with the student divers as this is the first time they perform it in open water,
4) directly supervise any remaining dive flexible skills requiring instructor supervision that haven’t been conducted in previous dives.
If there are no remaining dive flexible skills to be conducted by the instructor and the student divers have completed a safety stop with an instructor on an earlier open water dive, a certified assistant may supervise no more than two student divers under the indirect supervision of the instructor as the student divers carry out their dive plans, explore the dive site, ascend and make the required safety stop.
It may be that keeping all student divers together in one group under your direct supervision is your best choice; or, it may be that splitting the group into smaller teams of two student divers per instructor/certified assistant is best. As in any supervisory situation, make your choice considering all the variables present. In any case, this dive is the result of all that the student divers have learned, showcasing their ability to organize, plan and carry out a dive plan under close supervision.