Complex sentence: The organ sonatas, BWV 525--530 by Johann Sebastian Bach are a collection of of six sonatas in three movements with three independent parts, for two manuals and pedal.
Split into simpler sentences: The organ sonatas, BWV 525--530 by Johann Sebastian Bach are a collection of of six sonatas in trio sonata form. Each of the sonatas has three movements with three independent parts, for two manuals and pedal.