[Robert]'s mother [Nancy] made a cake for his birthday and her other son [Jacob] ate a piece of it.
('Robert', 'Jacob')
[Robert]'s mother [Nancy] made a cake for his birthday and her other son [Jacob] ate a piece of it.
[{('Robert', 'brother', 'Jacob'): [('Robert', 'mother', 'Nancy'), ('Nancy', 'son', 'Jacob')]}]
['mother', 'son']