Poseidon dwelt in the sea, where Zeus was a god of the sky, it was not that Zeus trusted either brother more then another, but he certainly saw Poseidon more often then Hades in his unseen underworld.
Both Hades and Poseidon causes trouble for Zeus,but Poseidon causes more trouble than Hades.
No, he keeps to the sea. Hades tries to overthrow Zeus to get more power, but he never suceeds
He was the one of the big three which consist of Zeus and Hades. He along with Zeus and Hades are the more powerful gods. He is god of the seas and of earthquakes and created horses.
No, he is just the god of the underworld. Hades had two brothers Zeus and Poseidon who ruled the Air and the Water respectively they were no more evil nor benevolent than Hades.
Hades was not a major deity in Greek mythology, Apollo and Athena were far more significant.
Zeus did not "send Hades to the Underworld"; just as Zeus rules the heavens, Hades rules the Underworld. According to one of the myths, Zeus selected the Heavens as his realm, and allowed Poseidon to select next because he was eldest. That left Hades (or more accurately Plouton) the Underworld as his realm, which he found suited him just fine.
Hades has never had any children. Zeus and Poseidon are probably still rather potent as they have proven to be in the past. I doubt they would agree never to reproduce again.
Zeus, Hades, and Poseidon, or the Big Three, swore on the River Styx, to no longer have demigod children, so when Zeus had Thalia, he broke his promise. Hades, angered that he broke his promise, sent horrible monsters after her.
Zeus,Hera,Poseidon,Demeter, Hestia were Hades's siblings. Hermes, Apollo, Artemis, Athena, Ares and Hephaestus his nephews. Aphrodite a more distant relative.
When Zeus steals the 5 sacred items, you have to get help from Poseidon and Hades. Hercules will finally help you if you have the Touchscreen mirror from Aphrodite. Travel to Hades and get the Hades Crown, then to Poseidon's realm to get his Trident. These two weapons will prove more than a match for Zeus. Hercules will get you past the locked gate and you can travel to Olympus. You will need the drachma from the Temple of Hades worker in order to climb Olympus. If you battle Zeus and win, you receive the Island Medallion. (see the related question)
It about the big three gods Zeus, Poseidon, and Hades read the books you will find out more
Greek mythology has more than three immortals, the gods themselves were immortal, such as Zeus, Hades and Poseidon.