Elendil only had two sons: Isildur & Anarion. The huge statues at the Gates of Argonath were built to honor them.
Goblins:
A name almost synonymous with Orcs. There is some debate about how closely the the two terms are related to one another, and indeed it could be argued that they both effectively relate to the same thing.
The following quote from the foreword to The Hobbit sheds some light on this: "[The word 'Orc'] occurs in one or two places but is usually translated goblin (or hobgoblin for the larger kinds.)' The fact that the larger kinds are given their own special word might suggest that goblins tend to be smaller Orcs, but the evidence on this point is inconclusive.
The word 'goblin' is also used occasionally and indiscriminately in The Lord of the Rings; it never occurs in the The Silmarillion.
Orcs:
Little is known for certain of the beginnings of the Orcs, the footsoldiers of the Enemy. It is said that they were in origin corrupted Elves captured by Melkor before the beginning of the First Age. In appearance, Orcs were squat, swarthy creatures. Most of them preferred the darkness, being blinded by the light of the Sun, but the kinds bred later in the Third Age such as the Uruk-hai could endure the daylight.
Azog: Cheiftan of the Northern Orcs:
An Orc-chieftain of Moria, who started the War of the Dwarves and Orcs when he slew Thrór. He was himself slain by Dáin Ironfoot in the Battle of Azanulbizar, and was succeeded by his son Bolg.
Of Azog's origins we know little; he was the chief of the Orcs of Moria, and apparently the most important Orc of the northern lands. The average lifespan of an Orc is unknown, but it is conceivable that he was one of those sent to Moria by Sauron in about III 2480. He had one son that we know of, Bolg, who succeeded him after his death.
Azog entered history in the year III 2790 due to King Thrór's desire to revisit and perhaps refound the lost realm of Khazad-dûm, in whose mighty ruins Azog dwelt. Azog captured and slew Thrór, and branded his hewn head with his own name, AZOG.
When news of this reached Thrór's heir Thráin, he was greatly angered, and mustered a force of Dwarves to seek revenge on Azog. So began the War of the Dwarves and Orcs: the Dwarves hunted Azog, and many battles were fought beneath the earth. After nine years of war, the climactic Battle of Azanulbizar was fought before the gates of Moria itself.
King Thráin and his son Thorin were in that battle (it was here that Thorin gained the surname Oakenshield). Near the end of the battle, Azog himself emerged and fought with Thráin's cousin Náin and, after breaking Náin's neck, his young son Dáin. Though only 32 years old, Dáin swept the head from Azog's shoulders, and helped to win the day.
The Dwarves made no attempt to press their advantage, though, because Dáin had glimpsed Durin's Bane during his battle, and warned the Dwarves not to attempt to enter Moria. Azog's underground dominions in the north, though greatly reduced in the War, fell to his son Bolg, who held them for more than 150 years until he too met his end at the Battle of Five Armies.
