docs: def getSiblings(self, textId: str, subreference: Union[str, BaseReference]) -> Tuple[BaseReference, BaseReference]:
          """ Retrieve the siblings of a textual node
  
          :param textId: CtsTextMetadata Identifier
          :type textId: str
          :param subreference: CapitainsCtsPassage Reference
          :type subreference: str
          :return: Tuple of references
          :rtype: (str, str)
          """
          raise NotImplementedError()