[Amy] and her sister [Lillian] went out to lunch with [Amy]'s sister [Nancy].
('Nancy', 'Lillian')
[Amy] and her sister [Lillian] went out to lunch with [Amy]'s sister [Nancy].
[{('Nancy', 'sister', 'Lillian'): [('Nancy', 'sister', 'Amy'), ('Amy', 'sister', 'Lillian')]}]
['sister', 'sister']