Profile sync using CiviCRM WordPress Profile Sync
Given that WordPress treats email addresses as unique identifiers, this situation is necessarily going to be problematic. There are a number of ways that you can overcome the default matching (which is handled by CiviCRM's CRM_Core_BAO_UFMatch::synchronizeUFMatch() method), but the simplest is to manually alter the record in the ufMatch table such that it points to the Civi record that you want it to. You can alternatively create the WordPress users from their CiviCRM contact records by using the bulk update functionality provided when you enable CIVICRM_WP_PROFILE_SYNC_BULK in the plugin. Or perhaps you could decide not to "forget that there may be methods of better organizing this"...