[Travis] went on a camping trip with his father [Dale] and grandfather [Clarence] last weekend.
('Dale', 'Clarence')
[Travis] went on a camping trip with his father [Dale] and grandfather [Clarence] last weekend.
[{('Dale', 'father', 'Clarence'): [('Dale', 'son', 'Travis'), ('Travis', 'grandfather', 'Clarence')]}]
['son', 'grandfather']