[George] took his sister [Nancy] to the zoo. [George] 'son [Douglas] did n't go because he is afraid of animals.
('Nancy', 'Douglas')
[George] took his sister [Nancy] to the zoo. [George] 'son [Douglas] did n't go because he is afraid of animals.
[{('Nancy', 'nephew', 'Douglas'): [('Nancy', 'brother', 'George'), ('George', 'son', 'Douglas')]}]
['brother', 'son']