So, in my fic, a few characters travel back in time quite a few years and drastically change the world.

My question is ...

What would happen after that? Would they have to live until they catch up with when they left, or would they be able to travel back forward in time and live in the new sort of world they created through the change? And on top of that, would they then - say they traveled back 5 years - be five years older? What would their memories be like? Would they remember the old past and their friends, seeing as the past would be different and they probably wouldn't have known each other.

I hope this didn't sound like nonsensical ramblings, but I'd really appreciate help.