[Lena] took her son [Chris] to [Lynn] ([Lena]'s sister) birthday party. [Chris] and his sister [Martha] are going for a walk.
('Lynn', 'Martha')
[Lena] took her son [Chris] to [Lynn] ([Lena]'s sister) birthday party. [Chris] and his sister [Martha] are going for a walk.
[{('Lynn', 'niece', 'Martha'): [('Lynn', 'sister', 'Lena'), ('Lena', 'daughter', 'Martha')]}, {('Lena', 'daughter', 'Martha'): [('Lena', 'son', 'Chris'), ('Chris', 'sister', 'Martha')]}]
['sister', 'son', 'sister']