on delete of one field delete other field too
You can use hook_field_delete to determine which field is removed, and if its "yours" - find out which field you need to delete next and delete it

function hook_field_delete($entity_type, $entity, $field, $instance, $langcode, &amp;$items) {
   if ($field['field_name'] == 'YOUR_FIELD_NAME') {
       //do some stuff to determine which
       //field you need to delete
       //and delete it 
       //how to remove the field - the link below
   }

}


how to remove the field