[April] and her sister [Andrea] went out to lunch with [April]'s sister [Ann].
('Ann', 'Andrea')
[April] and her sister [Andrea] went out to lunch with [April]'s sister [Ann].
[{('Ann', 'sister', 'Andrea'): [('Ann', 'sister', 'April'), ('April', 'sister', 'Andrea')]}]
['sister', 'sister']