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)

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()