Since apparently more discussion on the wraiths is here than elsewhere....
I don't see how these ghosts could be outright manifestations of Jenova itself or replacements of the Sephiroth Copies. That would entail a radical, fundamental change to the core plot of FFVII that would make this not a remake, but a complete remix.
However, I
do think they're connected to Sephiroth and Jenova. I mean, I don't think that's really a question at all, given the promotional artwork shown of him.
So what could they be?
Well... The whole situation reminded me of several things. First this event from the Early Material Files of FFVII.
The portion that explained what Sephiroth was doing in the Northern Crater.
[ Materia Chamber ] (* note: Inside the crater in the finished game)
A dome, filled with around 500 materia the size of a person lined up in a radial pattern. Among these are some even larger materia. In the centre is an energy crystal (Ultimate Materia), and inside that is a new life form. It resembles Sephiroth. However, its body is complete naked, and the contours of the body are closer to that of a woman’s.
Tifa: “So the one who is trying to crash Meteor into the planet and bring about a Big Bang…”
Vincent: “That is what Sephiroth, the new life form before us, desires. But he didn’t know the key to calling forth Meteor. Even after obtaining the knowledge of the Ancients that had fused into the mako energy, he wasn’t able to learn of it. In order to obtain the Black Materia, the secret to casting Meteor, he required someone who was able to move around freely.”
Tifa: “Jenova?”
Vincent: “No, not Jenova.”
...........
Inside the 500 materia, evil life forms (monsters) are now awakening.
Red XIII: “Sephiroth’s will must be very powerful. He has the power to draw out all the malevolent energy within the planet. That evil desire crystallized to form these materia. And he’s created soldiers to form an unholy army. You could say these materia are eggs waiting to hatch. With just the slightest shock the materia will shatter, and those devils will awaken.”
So in an unused storyline scenario, Sephiroth's very will and presence, was capable of drawing out and awakening evil energy from within the planet. It caused evil spirits to crystallize and form materia that would hatch and birth monsters that would be his "unholy army."
Now, compare that with what we know occurs in the original FFVII and Jenova.
Ifalna said...
Ifalna
That's when the one who injured the Planet... or the 'crisis from the sky', as we call him, came.
He first approached as a friend, deceived them, and finally...... gave them the virus.
The Cetra were attacked by the virus and went mad... transforming into monsters.
Ifalna describes how Jenova infected the Cetra with its virus which transformed them into monsters that attacked and killed everyone else. But, there's an interesting line she says
before that....
Ifalna
I'm all right... When the Cetra... were preparing to part with the land they loved...
That's when it appeared!
It looked like... our... our dead mothers... and our dead brothers. Showing us spectres of their past.
Gast
Who is the person that appeared at the North Cave? I haven't any idea.
Ifalna
That's when the one who injured the Planet... or the 'crisis from the sky', as we call him, came.
Now, not much attention was paid to that line since the focus was on Jenova's shapeshifting abilities that naturally could be used to mimic living or dead individuals. But the term, spectres of their past, sorta makes me think.
What if aside from shape-shifting, Jenova was
literally able to manipulate or summon evil spirits, or spectres of the dead to harass it's victims? Would that be possible?
In
Case of Lifestream Black, Sephiroth's spirit was able to manipulate and "mark" other spirits of those who died in hatred towards the planet. It was through these cursed souls he was able to create his own Negative Lifestream and further infect the living with Geostigma. Where did Sephiroth get this power from?
To me, it seems plausible, that the Remake is using the discarded concept that Sephiroth's presence and will in the Lifestream is a magnet for evil, tormented spirits that awaken and follow his presence as it manifests around either Jenova, Cloud or maybe Midgar itself.
The evil spirits are a sort of herald or omen of Sephiroth's re-awakened presence in the world as it begins to move and awaken Jenova in Midgar. Between Sephiroth's will tormenting Cloud, it would make sense if Sephiroth's will has a ripple effect across the Lifestream of the planet, stirring disembodied evil spirits within.
In the end it'd definitely allow the creators to have Sephiroth's depiction heavily lean in on being a "fallen angel" and utilize his presence more before he technically appears upon Cloud's arrival to the Shinra Building. His presence would be a growing threat to the planet that awakens evil and begins to cause Aerith torment. It'd also play up the connection that exists between Aerith and Sephiroth as polar opposites in regards to the planet.
That and everyone's theories, etc in the thread helped me feel better. As long as there is a balance. It's ok for our characters to show vulnerability, we're going to see Cloud's breakdown, Barret being upset about Coral, etc too. Also we might see something like this when Tifa falls in the lifestream too? That scene from the OG where she's in the dark at first and in distress, etc. Might be cool if Aerith shows up to help and touches Tifa and suddenly ghosts then too! 
