[Clarence] watched his son [Dale] play catch. [Dale] tossed the ball back and fourth with his brother [Nicholas].
('Clarence', 'Nicholas')
[Clarence] watched his son [Dale] play catch. [Dale] tossed the ball back and fourth with his brother [Nicholas].
[{('Clarence', 'son', 'Nicholas'): [('Clarence', 'son', 'Dale'), ('Dale', 'brother', 'Nicholas')]}]
['son', 'brother']