[John] and his son [Brent] went to the park and saw [John]'s father [Roy] there with his dog.
('Brent', 'Roy')
[John] and his son [Brent] went to the park and saw [John]'s father [Roy] there with his dog.
[{('Brent', 'grandfather', 'Roy'): [('Brent', 'father', 'John'), ('John', 'father', 'Roy')]}]