[Martha] and her brother [Charles] are taking [Martha]'s daughter [Lena] and [Lena]'s sister [David] to the beach for vacation.
('Charles', 'David')
[Martha] and her brother [Charles] are taking [Martha]'s daughter [Lena] and [Lena]'s sister [David] to the beach for vacation.
[{('Charles', 'aunt', 'David'): [('Charles', 'mother', 'Lena'), ('Lena', 'sister', 'David')]}, {('Charles', 'mother', 'Lena'): [('Charles', 'sister', 'Martha'), ('Martha', 'mother', 'Lena')]}]
['sister', 'mother', 'sister']