A complete leap of logic, not supported by one word in the bible. Union of the saints with God is never indicative of the communication of the divine properties of omni-presence or omniscience (all knowledge) of God. If so, saints in heaven would not be asking God questions (as they do in Rev. 6:10).
Besides that, in spite of all the detailed instructions on how to live the Christian life to the new Christian churches in the New Testament, there is not one word recommending praying or communicating to saints in Heaven.
One would think, that if it is possible to communicate with dead Christians, and highly recommended--Saint's Paul and Peter would have talked about it--but, they did not.
The Old Testament prohibitions against trying to communicate with the dead , necromancy, still apply--as there is no indication that these moral laws have been completed or revoked: "Let no one be found among you who...is a medium or spiritist or who consults the dead. Anyone who does these things is detestable to the LORD, and because of these detestable practices the LORD your God will drive out those nations before you." (Deut 18:10-12)
Strong language? Yes, and a command Rome has ignored, tolerated and encouraged disobedience to for many hundreds of years--to her peril.
So, do you believe that those people in heaven are alive ans praising God as witnessed by John in Revelation?
I do. And if they are heavenly beings alive with the angels and the elders that John saw in that vision, then I believe they can hear our prayers when we ask them to pray for us or help us.
Do you believe that Christ is also dead? Or do you believe that He is alive in Heaven? Ame comparison, correct?