[Dale] met his son [Nicolas] for dinner. Unfortunately [Dale]'s son [Tony] could not attend.
('Tony', 'Nicolas')
[Dale] met his son [Nicolas] for dinner. Unfortunately [Dale]'s son [Tony] could not attend.
[{('Tony', 'brother', 'Nicolas'): [('Tony', 'father', 'Dale'), ('Dale', 'son', 'Nicolas')]}]
['father', 'son']