YES THEY DID!!!!

The Nephilim, also known as the Grigori or Watchers, are believed to be the children from the union  between angels and human women.

"When men began to increase on earth and daughters were born to them, the divine beings saw how beautiful the daughters of men were and they took wives from among those that pleased them. It was then, and later too, that the Nephilim appeared on earth - when the divine beings cohabited with the daughters of men, who bore them offspring. They were the heroes of old, the men of renown.” (Genesis 6:2-4.)

Read more here and here and here.

They were the titans, pans, gods, goddesses, pharaohs, and fawns of Greek and Roman mythology, emperors, priests, shamans....they ruled over mankind and corrupted them.

2. How did they die? 

God sent the angel Gabriel to incite them against each other.  Read more here.

Book of Jubilees (ancient Jewish religious work) (7:21-25) also states that ridding the Earth of these Nephilim was one of God's purposes for flooding the Earth in Noah's time.

3. Do they still live among us?  YES!!

Genesis 6:4: The Nephilim were upon the Earth in those days and thereafter too. Those sons of the gods who cohabited with the daughters of the Adam, and they bore children into them. They were the Mighty Ones of Eternity, the People of the Shem.

This seems to clearly imply that the Nephilim were also on the Earth after the flood of Noah.

According to the Book of Enoch (work ascribed to Enoch, the great-grandfather of Noah and son of Jared, God granted ten percent of the disembodied spirits of the Nephilim to remain after the flood, as demons, to try to lead the human race astray

4. Myths.

Are the Nephilim behind UFOs, Atlanteans, vampires and werewolves?