I'll just post the thatching-part thing.
Basically, for parting double-sided hair and making it look good, you have to take each individual plug and pull it to the other side. You're weaving it, to be simple. Mind you, you have to do every single plug, or it won't look very good. I recommend you have a thin thing that can divide while you grab. I just used my fingernail, but as most of you don't grow out your nails like I do, as I'm a girl, I'd recommend a piece of cardstock or even tweezers. It takes forever and it's easy to mess up if you've just started, so I recommend putting the divided hair into ponytails and taking breaks. When I did her hair, I took breaks between each color of her hair. The good thing is, though, is that when you finally finish, it more likely than not won't go back to its undivided state.
If you want to be sure the thatching stays, just pour boiling water on it while holding it so the thatching faces the stream of water.