[Theodore] went skiing with his brother, [Chris], and his sister, [Martha]. [Martha]'s grandmother [Frances] had purchased the group an all-inclusive ski vacation.
('Chris', 'Frances')
[Theodore] went skiing with his brother, [Chris], and his sister, [Martha]. [Martha]'s grandmother [Frances] had purchased the group an all-inclusive ski vacation.
[{('Chris', 'grandmother', 'Frances'): [('Chris', 'sister', 'Martha'), ('Martha', 'grandmother', 'Frances')]}, {('Chris', 'sister', 'Martha'): [('Chris', 'brother', 'Theodore'), ('Theodore', 'sister', 'Martha')]}]
['brother', 'sister', 'grandmother']