[John] is in the same grade as his sister [Ann], but his sister [Janet] is 2 years ahead of him.
('Ann', 'Janet')
[John] is in the same grade as his sister [Ann], but his sister [Janet] is 2 years ahead of him.
[{('Ann', 'sister', 'Janet'): [('Ann', 'brother', 'John'), ('John', 'sister', 'Janet')]}]
['brother', 'sister']