In 1999, my book The Sibling Constellation: the Astrology and Psychology of Sisters and Brothers was published by Penguin Arkana in the UK. It is now out of print. The astrology section has been revised and reprinted in the Student Booklet Series called the Astrology of Brothers and Sisters which you can find here: www.astrosynthesis.com.au/student-astrology-ebooklets/
I was fascinated that the development of psychology in the early 20th century with Pluto in Gemini had overlooked the sibling. As I researched its founding fathers, it became clear that all three had lost a brother, just like the mythic twins of Gemini: Pollux had lost his brother Castor. The following 3 astrology articles are Alfred Adler’s, Carl Jung’s and Sigmund Freud’s sibling stories and their horoscopes.