[John] took his sister [Janet] out to dinner for her birthday. [John] and his brother [Douglas] went to the football game together.
('Janet', 'Douglas')
[John] took his sister [Janet] out to dinner for her birthday. [John] and his brother [Douglas] went to the football game together.
[{('Janet', 'brother', 'Douglas'): [('Janet', 'brother', 'John'), ('John', 'brother', 'Douglas')]}]
['brother', 'brother']