Well Sephiroth is definitely either a time-traveler or is able to use the lifestream to see the future.

I didn't think Aerith was though. I thought she was just using her ability to communicate with the planet to essentially ask what's going on. Because she seems clueless at the very start, but then suddenly knows a lot more when you see her in the church.

Although now I think of it, I guess that's kinda the equivalent of just using the lifestream to see the future.