Following "conventional" rules of time travel, there will be no "future" John and Sarah in 2007 because they never go back to 1999 (was it 1999?).
But if, for example, their trip to 2007 was only temporary and they go back to 1999, then, 8 years later, they might see their "past" selves running around in 2007.
It's hard to explain, hope I made some sense.