Complex sentence: In 1903, A.E. Waite and Blackden joined forces to retain the name Isis-Urania, while Felkin and other London members formed the Stella Matutina, Yeats remaining in it until 1921, and Brodie-Innes continued his Amen-Ra temple in Edinburgh.
Split into simpler sentences: In 1903, A.E. Waite and Blackden joined forces to retain the name Isis-Urania, while Felkin and other London members formed the Stella Matutina. Yeats remained in the Stella Matutina until 1921, while Brodie-Innes continued his Amen-Ra membership in Edinburgh.