Complex sentence: Alexander Chekrygin (who joined the project in 1903), and Victor Rakhmanov (who joined the project in 1904)--both of whom were former danseurs with the St. Petersburg Imperial Theatres.
Split into simpler sentences: Alexander Chekrygin (who joined the project in 1903) and Victor Rakhmanov (who joined the project in 1904). Both Chekrygin and Rakhmanov were former danseurs with the St. Petersburg Imperial Theatres.