There’s nothing in the Bible about the spirits of some dead humans “staying behind” on earth. Spirits return to God (Eccl. 12:7). Eccl 9:5 says that the dead don’t know anything (of what is happening on earth); several passages in Psalms echo that teaching. Job says that, had he been stillborn, his spirit would be with all other spirits including those of kings, counselors, princes, prisoners, masters and servants; and there’s no more earthly trouble in that place (Job 3:11-19). Whether it’s a real-life account or a parable, Jesus' story of Lazarus and the Rich Man in Luke 16:19-31 emphasizes that the dead aren’t allowed to return to earth.

The only exception to this rule is found in I Sam. 28:3-20. Because God no longer answered wicked King Saul’s prayers, Saul sought out a woman [of Endor] with a familiar spirit (in other words, demon-possessed). That wasn’t easy, because when Saul was right with God, he himself had gotten rid of such people in obedience to Ex. 22:18 and Deut. 18:9-12. But he found one. She didn’t object or react when he asked her to bring up Samuel for him, but when Samuel actually DID come up, she cried out, and correctly guessed that her customer was Saul.

It would seem that she (like any other medium) was going to bring forth a demon spirit who would imitate Samuel; and when she saw the REAL Samuel, she knew something was happening that was out of her control. Why God made this exception to His own rule is His business, not ours. The point is that it clearly is an EXCEPTION.

The magician and escape artist, Harry Houdini, visited so-called spirit mediums in every city where he toured, hoping to contact his deceased loved ones; but invariably he recognized that those “mediums” were using stage-magic, and he exposed them as frauds. We can safely assume that the same is true today; almost all such people are hucksters, a few might use demon power, but none are what they say they are. The only way to see your dead loved ones again is to meet them in the Kingdom of God.

As for the idea of controlling malevolent spirits (who are demons, not the spirits of the dead) with incantations, that’s pure witchcraft and extremely dangerous. The only word evil spirits are subject to is the Name of Jesus (Mark 16:17; Luke 10:17); and things might go badly for someone who tries to use that name but doesn’t KNOW Jesus (Acts 19:11-20).

For spiritual battles, what we need is the power of God. See Eph. 6:10-17 and 2 Cor. 10:3-4.