Complex sentence: Irene next had to subdue a rebellion led by Elpidius, the "strategos" of Sicily, whose family was tortured and imprisoned when a fleet was sent, which succeeded in defeating the Sicilians.
Split into simpler sentences: Irene next had to subdue a rebellion led by Elpidius, the "strategos" of Sicily. Irene sent a fleet, which succeeded in defeating the Sicilians.