Joan and Jackie Collins - Joan, the eldest, gained fame as Alexis Carrington Colby on television's Dynasty. Jackie tried and failed to start a film career, but found great success as a writer of romance novels.
After being diagnosed with the autoimmune disease Sjogren's Syndrome, professional tennis player Venus Williams switched to a raw, vegan diet. Her sister Serena Williams switched as well, for moral support.
The York sisters. Princesses Margaret Rose (left) and Elizabeth of York, daughters of the future George VI. At this time in their lives their uncle, Prince Edward, was still the heir apparent and the sisters were headed for a life of relative obscurity ("obscure" that is, for members of the world's most famous royal family).