The brothers of Zeus were Poseidon and Hades.
Poseidon was the god of the sea, while Hades ruled over the underworld. Both brothers were powerful Olympians.
Zeus had one half brother, the centaur, Chiron.
Hades
Hades was the god of the underworld in Greek mythology. He was the son of Cronus and Rhea, and was brother to Zeus and Poseidon. Hades was not particularly popular among the gods, and was often referred to as the “lord of the dead”. He was feared by mortals because of his role as a judge of the dead, and because he had the power to send them to the underworld. Hades was also known for his role in the abduction of Persephone, which led to her becoming his queen.
In art, Hades is often portrayed as a dark-haired man with a beard, wearing a crown of laurels and holding a staff. He may also be shown with a drinking horn or cup, as he was the god of wine. Hades is sometimes portrayed in a chariot drawn by black horses, or with Cerberus, the three-headed dog who guarded the entrance to the underworld.
Hades was not worshipped as frequently as other Greek gods, but there were temples and shrines dedicated to him, particularly in the regions of Greece where he was most associated with the underworld. Animal sacrifices were often made to Hades, and black animals were especially favored. Gifts of food and drink were also common offerings to the god.
The festival of the Anthesteria was dedicated to Hades, and included a number of rituals involving wine.
Poseidon
Poseidon was the god of the sea in Greek mythology. He was the son of Cronus and Rhea, and was brother to Zeus and Hades.
Poseidon was especially popular among sailors, as he was said to protect them from storms and other dangers at sea. He was also the god of earthquakes, and was often depicted holding a trident.
Poseidon was usually portrayed as a bearded man with curly hair, wearing a tunic and crown of laurels. He might also be shown riding in a chariot drawn by sea creatures, or holding a fish or dolphin. In art, Poseidon is often shown with his attributes, the trident and dolphins. He is also sometimes shown with a horse, as he was the god of horses as well as the sea.
Poseidon had temples and shrines dedicated to him throughout Greece, but was especially revered in coastal regions. Animal sacrifices, particularly of bulls and horses, were common offerings to Poseidon.
The festival of the Panathenaea, which was dedicated to Athena, also included sacrifices to Poseidon.
Chiron
Chiron was a centaur in Greek mythology. He was the son of Cronus and Philyra, and was half-brother to Zeus, Poseidon and Hades. Chiron was known for his wisdom and healing abilities. He was also an expert archer, and taught both Hercules and Achilles how to use a bow and arrow.
Chiron was usually portrayed as a bearded man with the body of a horse. He was sometimes shown holding a bow and arrow, or teaching one of his students. In art, Chiron is often shown alongside animals, as he was especially associated with horses and deer.
Chiron had a temple on Mount Pelion in Greece, where he was worshipped as a god of healing. Animal sacrifices, particularly of horses and deer, were common offerings to Chiron.