[George] took a cab to the mall with his sister [Theresa]. [Theresa]'s sister [Nancy] drove herself there.
('Nancy', 'George')
[George] took a cab to the mall with his sister [Theresa]. [Theresa]'s sister [Nancy] drove herself there.
[{('Nancy', 'brother', 'George'): [('Nancy', 'sister', 'Theresa'), ('Theresa', 'brother', 'George')]}]
['sister', 'brother']