You would need to update the staff member's configured setting for receiving order emails in order to disable it. This is only possible when logged in as that particular staff member and going to the Orders widget. Alternatively, you could update the database to remove them from the list in the interim: under the `order_staff_settings` table, you can find records for that staff member by his staff ID, then update the `value` column to "never" for the `key`s "email_notice" and "mobile_notice".
This issue will be resolved in CORE-1905.