code: def getSiblings(self, textId, subreference):
          
          key = _cache_key("Nautilus", self.name, "Siblings", textId, subreference)
          o = self.cache.get(key)
          if o is not None:
              return o
          passage = self.getTextualNode(textId, subreference, prevnext=True)
          siblings = passage.siblingsId
          self.cache.set(key, siblings)
          return siblings
docs: Retrieve the siblings of a textual node
  
          :param textId: PrototypeText Identifier
          :type textId: str
          :param subreference: Passage Reference
          :type subreference: str
          :return: Tuple of references
          :rtype: (str, str)