So here I am, one of the three Watson sisters going into Salem this term. Here's the family information as it stands now (follow the bolded lines):
Jacques Vartan b. 1797 d. 1887 (Gryffindor) married Renee Deschamps b. 1826 d. 1905 (Beauxbatons Transfer to Hogwarts - Hufflepuff)
Jacques' and Renee's children
Joseph Vartan b. 1827 d. 1900 (Gryffindor) married Tracy Owens b. 1829 d. 1905 (Gryffindor)
Pierre Vartan b. 1825 d. 1889
Joseph's and Tracy's children
Nicholas Vartan b. 1857 d. 1916 (Gryffindor) married Louise Moore b. 1859 (Gryffindor)
Mary Jane Vartan b. 1862 (Gryffindor) married Stephane Mayer b. 1864 (Durmstrang Transfer to Hogwarts - Ravenclaw)
Daniel Vartan b. 1864 (Gryffindor) married Georgia Driscoll b. 1863 (Hufflepuff)
Mary Jane's and Stephane's children
Sylvia Mayer b. 1887 (Durmstrang Transfer to Hogwarts - Gryffindor) married Mark Randall b. 1885 (Hufflepuff) divorced 1925
Josephine Mayer b. 1889 (Durmstrang) married Patrick Kynan O’Connors b. 1891 (Durmstrang)
Adrienne Mayer b. 1898 (Ravenclaw) married Jonathan Watson b. 1895 (Salem)
Adrienne's and Jonathan's children
Naomi Mary Watson b. April 24th 1925 (Salem) - taken
Rachel Annette Watson b. July 4th 1926 (Salem) - taken
Sylvia Bernadette Watson b. June 19th 1927 (Salem) - taken
EDIT - All sisters have been taken.
As far as the parents are concerned, Adrienne is a Healer and owns a private practice in Boston. Jonathan is a Potions Professor at Northeastern Wizarding College in Boston. The Watsons live in Newport, Rhode Island.
The family is quite wealthy, hence why the three girls are acting like spoiled brats most of the time, a common personality trait for all of them.