[Glen] and his brother, [Dennis], went to visit [Glen]'s grandfather, [Clarence].
('Dennis', 'Clarence')
[Glen] and his brother, [Dennis], went to visit [Glen]'s grandfather, [Clarence].
[{('Dennis', 'grandfather', 'Clarence'): [('Dennis', 'brother', 'Glen'), ('Glen', 'grandfather', 'Clarence')]}]
['brother', 'grandfather']