WILLIAMSTOWN — In one biography of Georgia O’Keeffe, the famed artist’s four sisters are mentioned only in passing, as though her family was incidental to her success as an artist.In the novel “Georgia,” by Dawn Tripp, the sisters only dabble in art. Catherine is a fulfilled mother, Claudia a teacher, Anita a society wife, and Ida a full-time nurse.In fact, both Catherine and Ida showed artistic talent, but Georgia pressured them to stop [...]