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