She can not be born in Dec 1900 as the census was taken Jun 15 1900.........This makes her birthdate Dec 1899........Check the brth recxords on www.stevemorse.org
...she was born Dec 30th 1899....
C) Anna C Anderson born Dec 1900 in Brooklyn, Kings, New York, USA. *I would love her actual date of birth, her middle name, who she married, if she had children and when she died.
Additionally you state Anders mafus Anderson died in 1913..His death recrd shows his fiorst name as Magnus. If you get hus death certificate it will tell you where he is buried among other thigs. This may lead to John W )aka your William A) and ana/aie. Good luck