[Lillian] brought her son [Douglas] and her father [Clarence] to the farmer's market.
('Douglas', 'Clarence')
[Lillian] brought her son [Douglas] and her father [Clarence] to the farmer's market.
[{('Douglas', 'grandfather', 'Clarence'): [('Douglas', 'mother', 'Lillian'), ('Lillian', 'father', 'Clarence')]}]
['mother', 'father']