[Douglas]'s mother [Lillian] bought a Christmas gift for his sister, [Ann].
('Ann', 'Lillian')
[Douglas]'s mother [Lillian] bought a Christmas gift for his sister, [Ann].
[{('Ann', 'mother', 'Lillian'): [('Ann', 'brother', 'Douglas'), ('Douglas', 'mother', 'Lillian')]}]
['brother', 'mother']