[Lena]'s father [James] and sister [David] joined her for her hike. [David]'s son, [Bobby], could n't make it because of work.
('Bobby', 'James')
[Lena]'s father [James] and sister [David] joined her for her hike. [David]'s son, [Bobby], could n't make it because of work.
[{('Bobby', 'grandfather', 'James'): [('Bobby', 'mother', 'David'), ('David', 'father', 'James')]}, {('David', 'father', 'James'): [('David', 'sister', 'Lena'), ('Lena', 'father', 'James')]}]
['mother', 'sister', 'father']