The 3rd and 4th book happen "simultaneously" (i.e. in the same time period, but it's not mirrored so the beg of book 3 is the same time as the beg of book 4, and the endings aren't necessarily at the same exact date), they just have different characters.
So I was under the impression the 3rd and 4th season of the TV show would be encompassing both the 3rd and 4th book at the same time