Complex sentence: Then Zeus released the brothers of Cronus, the Gigantes, the Hecatonkheires, and the Cyclopes, who gave him thunder and lightning, which had previously been hidden by Gaia; then with these new allies and his siblings, Zeus overthrew Cronus and the other Titans.
Split into simpler sentences: Then Zeus released the brothers of Cronus, the Gigantes, the Hecatonkheires, and the Cyclopes, who gave him thunder and lightning, which had previously been hidden by Gaia. Zeus and his siblings, together with the Gigantes, Hecatonkheires, and Cyclopes, overthrew Cronus and the other Titans.