code: def get_siblings(self, objectId, subreference, passage):
          
          reffs = [reff for reff, _ in self.get_reffs(objectId)]
          if subreference in reffs:
              index = reffs.index(subreference)
              # Not the first item and not the last one
              if 0 < index < len(reffs) - 1:
                  return reffs[index-1], reffs[index+1]
              elif index == 0 and index < len(reffs) - 1:
                  return None, reffs[1]
              elif index > 0 and index == len(reffs) - 1:
                  return reffs[index-1], None
              else:
                  return None, None
          else:
              return passage.siblingsId
docs: Get siblings of a browsed subreference
  
          .. note:: Since 1.0.0c, there is no more prevnext dict. Nemo uses the list of original\
          chunked references to retrieve next and previous, or simply relies on the resolver to get siblings\
          when the subreference is not found in given original chunks.
  
          :param objectId: Id of the object
          :param subreference: Subreference of the object
          :param passage: Current Passage
          :return: Previous and next references
          :rtype: (str, str)