The pre-hellenistic interpretation of the few mentions of Sheol and the rephaim are vague and varied.
While the "interpretation" might have been vague or varied, the Scriptures referencing them are not. A reasonable person would be hard pressed to make the case for annihilationism, even in the OT, that at death all that is man becomes extinct as the JWs teach incorrectly, to be reasembled in the future, and that no conscious immaterial entity soul (spirit) survives the death of the body. Add the proof texts of the NT and annihilationism crumbles, as does soul materialism, a major platform of Watchtower pseudo-theology.
You forgot to mention the 'owb.' That the departed dead spirits in Sheol are conscious and communicate and think is reiterated at Isaiah 29:4 (KJV) where God warned the inhabitants of Jerusalem of their impending destruction, writing through the prophet, “Prostrate you shall speak from the earth, and from the base dust your words shall come. Your voice shall be like a ghost's (Hebrew, owb) (Vine's at 178), from the earth, and your words like chirping from the dust.” (NAB). According to Vine's, “Owb means 'spirit' (of the dead); necromancy, pit. This word usually represents the troubled spirit (or spirits) of the dead. This meaning appears unquestionably in Isaiah 29:4” (ibid.).
The Jehovah's Witnesses are technically “materialists” and subscribe to the doctrine of materialism (not to be confused with greed and the accumulation of things). Materialists deny body/soul dualism and the very existence of a “soul.” They believe all cognitive functions of thought, emotions, will and conscience, etc. are biological consequences of the material self, the body. When the body dies, that which traditionalists call the soul (spirit) simply vanishes and ceases to exist. “For the materialists, the soul, or the conscious life, is but a function of the organism, and necessarily perishes at death” (www.newadvent.org/cathen/07687a.htm).
Materialism is not unique to the Watchtower Society. It can be traced back to the Greek philosopher Epicurus (341-270 B.C.) who taught, among other things, that nothing exists except matter and space (PBD at 256). Epicurus believed that ... he could disprove the possibility of the soul's survival after death Stanford Encyclopedia of Philosophy, http://plato.stanford.edu/entries/epicurus/. Furthermore, “[t]he Epicurean school offers us the most complete and reasoned negation of immortality among ancient philosophers” (newadvent.org/cathen/07687 at 3). Epicureanism was widespread and popular during the time of Christ, and it is logical to conclude that the Jehovah's Witnesses' doctrine of materialism is rooted in this Greek philosophy.
Similarly, the ancient Sadducees, a religious party that existed during the time of Christ and which had members in the Jewish council called the Sanhedrin (which caused Christ to be put to death) denied “personal immortality, and retribution in a future life (PBD at 741), just like the Jehovah's Witnesses. “The doctrine of the Sadducees,” wrote Josephus,” is this, that souls die with the bodies,” (Antiq. Xviii. 1, 4); and again, “they also take away the belief of the immortal duration of the soul, and the punishments and rewards in Hades” (Jewish War, ii,i,14) (PBD at 741), just as the Jehovah's Witnesses teach.
In contemporary times the Jehovah's Witnesses are allied with secular atheists and other non-Christians on the margins who go to great lengths to deny the existence of the Christian immortal soul, or any soul for that matter, claiming that the soul is nothing more than the product of an organism, secretions of the brain and such, basing their claims in part on “neurophysiology,” (Restoring the Soul to Christianity, DR 502, J.P. Moreland, http://www.equip.org/articles/restoring-the-soul-to-christianity/).
Lastly, there has been a recent rash of materialist apologetics – evangelical preachers – who argue that Christian body/soul dualism is false, that a person is not a composite of body and soul, that the soul does not survive the death of the body, and the resurrected unsaved wicked are not punished eternally, or at all, but are simply extinguished, annihilated, being treated to a kinder, gentler, one-size-fits-all form of punishment. Of course it is no surprise that such modern-day preachers are attempting to overturn 2,000 years of Christian theology, for the Bible warns us that “in the last days, false teachers and false prophets will appear among us (2 Peter 2:1; Matthew 24:11).