[Robert]'s mother, [Nancy], was calling him for dinner. [Kevin] and his brother [Robert] were playing tag in the park.
('Kevin', 'Nancy')
[Kevin] and his brother [Robert] were playing tag in the park. [Robert]'s mother, [Nancy], was calling him for dinner.
[{('Kevin', 'mother', 'Nancy'): [('Kevin', 'brother', 'Robert'), ('Robert', 'mother', 'Nancy')]}]
['brother', 'mother']