[Nicholas] invited his sister [Theresa] to dinner. [Nicholas]'s brother [George] was too busy to attend.
('George', 'Theresa')
[Nicholas] invited his sister [Theresa] to dinner. [Nicholas]'s brother [George] was too busy to attend.
[{('George', 'sister', 'Theresa'): [('George', 'brother', 'Nicholas'), ('Nicholas', 'sister', 'Theresa')]}]
['brother', 'sister']