How to make scattered path following for a tower defense game? And a diverging path?

I'm trying to create a simple Tower Defense game for fun and I'm not sure how to approach creeps moving along a path.

It's easy to create an actual "path" that GM offers, and make creeps follow that path. But what if I want the creeps to follow the road but not exactly on top of that path? I want them to be scattered, to cover most of the road, like so: http://i.imgur.com/AlwqV6Y.png

Can I make them follow a GM's path imprecisely and offset? Should I create a different slightly offset path for each creep? Is creating many paths like that taxing? Or should I do it differently, without using paths? But how?

Also, if I want diverging paths like so: http://i.imgur.com/80uP0At.png How can I achieve that using paths? I assume one path can't be split like that, so there would have to be another one at the crossroads, into which creeps switch, right? Maybe a hidden object that once they collide with tells them in which way to go. But what about with no paths?

Thanks for your time