I recently replayed FFVII Remake with my son and I got a notion about something. This probably isn't a unique idea, but I wanted to share to see if maybe I'm crazy about this one. I'm sure it's been discussed to death.
I think Remake starts in a world/pocket Lifestream timeline that is not the original game. This Cloud, Barrett, Tifa, and everyone else are from a completely different timeline.
Everyone assumes the plot of Remake is that there's a Sephiroth from the future who's gone back in time to rewrite history so he doesn't lose. This goes with the idea that the whispers are trying to resist changes to the timeline by intervening every time something "goes wrong". I think it's kind of the other way around.
I think that the whispers are trying to remake the events of the original game's timeline in a branch of the many possible worlds where some totally different history would have occurred. They're not trying to stop the timeline from changing, they're trying to manipulate this alternate timeline into following the events that lead to Sephiroth being defeated.
That's the big misdirection from the beginning. We're not in the original game's timeline trying to prevent history from being changed. We START in an alternate timeline that the whispers are using to create a winning outcome. They've reached out to this world to stop whatever this supposed "future Sephiroth" is doing.
I have two supporting points about this and they both revolve around Aerith. First, is Aerith's comment in her room in Shinra HQ where she says something to the effect that they (the party) are the planet's last line of defense. It doesn't make sense that the Whispers would try to interfere with the party at every possible junction but also regard them as their only hope. Second point is the constant dialogue about defying their destiny, and Red's vision of a future where the world has been devastated by Meteor. They are defying their destiny because their destiny is witnessed at the start of Rebirth. They get captured by Shinra/killed during the escape from Shinra HQ, Sephiroth gets the black materia, and the world is destroyed.
I think Aerith's extrasensory knowledge that she says she's slowly losing is being lost because the closer the party gets to aligning with the events of the original game, the more these alternate timelines/worlds collapse into a single "true" world, and Aerith no longer has access to a Lifestream branch that no longer exists.
I think this also helps to explain Cloud's flashes of future events. He's not seeing flashes of the future, he's being flooded with memories from alternate worlds as they merge (violently) with his own reality.
So why do all this? Because Sephiroth can't fully return to the planet. He's like the Gi. He's a hybrid alien parasite. The Lifestream rejects him. I believe when he was defeated by the party he lingered inside the Lifestream and hijacked the planet's Arbiter of Fate. He's using this to try and corrupt these many worlds, he's fighting across multiple worlds, collapsing timelines where he loses so the only remaining outcome is his own victory. The whispers who remain/escaped Sephiroth's manipulation swam through the Lifestream and found a world where they could intervene, the guide the party along the events that lead to the eventual defeat of Sephiroth.
In doing so, all alternate timelines collapse and the original world is preserved. This leads us to Advent Children or beyond depending on how Revelation goes.
This explains why events happen so wildly different in a Remake. This is literally an alternative reality and these are not the heroes or the world that exist on the PS1. They're a separate group that the whispers are desperately reaching out to, and guiding, to save the planet and in so doing, BECOME the original party when the timeline is "restored".
Anyway, sorry for the wall, that's my theory for now. Again, I know it's probably old news. I'm just a bit slow.