[Douglas] took his mother [Lillian] and his sister [Janet] out to lunch.
('Lillian', 'Janet')
[Douglas] took his mother [Lillian] and his sister [Janet] out to lunch.
[{('Lillian', 'daughter', 'Janet'): [('Lillian', 'son', 'Douglas'), ('Douglas', 'sister', 'Janet')]}]
['son', 'sister']