[Dennis] and his sister [Mary] were twins. Still, they did n't look very much alike. [Nicholas] and his son [Dennis] went to the store to by bread.
('Nicholas', 'Mary')
[Nicholas] and his son [Dennis] went to the store to by bread. [Dennis] and his sister [Mary] were twins. Still, they did n't look very much alike.
[{('Nicholas', 'daughter', 'Mary'): [('Nicholas', 'son', 'Dennis'), ('Dennis', 'sister', 'Mary')]}]
['son', 'sister']