I'm pretty sure they're taking parts from both AFFC and ADWD. I also heard they might be spoiling some stuff that's going to be in Winds of Winter. Hopefully nothing too dramatic.
I heard that they were conferring with Martin about what would bein Winds of Winter, so that they could hint and possible evens that'd occur, but not actually filming it.
And yes, they will take from both book 4 and 5. This being because book 4 and five were originally the same book, but due to having too much text, Martin had to split them up.
I'd guess we will see the next season being both Book 4 and 5 as well.