19 Now if people say to you, “Consult the ghosts and the familiar spirits that chirp and mutter; should not a people consult their gods, the dead on behalf of the living, 20 for teaching and for instruction?” Isaiah 8:19
There are a couple things wrong with your conclusion. One is that the saints in heaven are not “dead”. As Jesus says, they are alive forevermore.
" Jesus said to them, “Is not this the reason you are wrong, that you know neither the scriptures nor the power of God? 25 For when they rise from the dead, they neither marry nor are given in marriage, but are like angels in heaven. 26 And as for the dead being raised, have you not read in the book of Moses, in the story about the bush, how God said to him, ‘I am the God of Abraham, the God of Isaac, and the God of Jacob’? 27 He is God not of the dead, but of the living; you are quite wrong.” Mark 12
1 John 2:17 And the world and its desire are passing away, but those who do the will of God live forever.
John 6:58 This is the bread that came down from heaven, not like that which your ancestors ate, and they died. But the one who eats this bread will live forever.”
"…they cried out with a loud voice, “Sovereign Lord, holy and true, how long will it be before you judge and avenge our blood on the inhabitants of the earth?” Revelation 6:10
These martyrs that cry out to God for justice upon those who murdered them are not ghosts, familiar spirits that chirp and mutter; “gods” or dead! They are living saints in heaven, and they are aware of what is happening here on earth.
Moses and Elijah, who met with Jesus at the Transfiguration and had a little chat with Him about his upcoming “departure” were also aware of what was happening, and about to happen. Jesus gives us an example in showing His disciples that the communion of saints is continuous - not separated by death.