Are you speaking of the doctrine that man has an eternal spirit? Or are you asking if Abraham and other patriarchs and/or prophets are now in Heaven?
Regarding the latter, Heaven, as it pertains to us, is not yet in existence. It is what the earth will become after our resurrections. The inhabitants of the earth were first destroyed by water, which symbolized its baptism. Next, it will be cleansed by fire, which represents the baptism of fire and the Holy Spirit. Finally, at the end of the Millennium, this world will go through a “death” and “resurrection” of its own. After the former, the earth will be instantly transformed into the abode of the righteous. There will be no “paradise earth” with gardens and eternal picnics and family reunions that will last forever. Man’s resurrection, according to the apostle John, will be glorious and like unto the Savior’s resurrection. The earth will be radiating glory, and those inhabiting it will be beings of incredible light and glory. The idea that man will go back to being like Adam and Eve is incredibly WRONG. As the Greek Orthodox teach, “Jesus became as we are so that we might become as he is.” That’s why Adam and Eve fell, so that, through Christ, we might take a giant leap upward and become one with Christ and the Father. In short, the Father had every intention that man would fall. And through Jesus, we might not again become as Adam, but become as Christ in power and light, inheriting all that the Father has.
If God the Father is God, and Jesus Christ is God, and we can be one with them, then we have incredible potential. But as Paul wrote: “Furthermore we have had fathers of our flesh which corrected us, and we gave them reverence: shall we not much rather be in subjection unto the father of spirits, and live?” (Hebrews 12:9) Also: “The Spirit itself beareth witness with our spirit, that we are the children of god: and if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us. (Romans 8:14-18)
For the Jehovah's Witnesses to believe that man has no spirit, how do they reconcile the above? The prophet Zechariah wrote: “ The burden of the word of the Lord for Israel, saith the Lord , which stretcheth forth the heavens, and layeth the foundation of the earth, and formeth the spirit of man within him. ” (Zech. 12:1)
I cannot conceive of God being the father of “breaths” instead of spirits. Or forming the “breath” of man within him. True, the word breath in both Hebrew and Greek can mean either breath or spirit. One must use context to differentiate between the two in any given passage, and most Christians (and Jews) in many cases translates the words “spirit” while the Adventists, many times in the face of overwhelming logic, do just the reverse. In school we covered both interpretations in the various languages and passages, and while people on both sides of the issue can push their interpretations, our professor said, the Adventists are in the distinct minority.