On a wagon, you will have to drop both the Front and rear headliners. Here's the steps in general (special tools required mostly panel poppers):
1. remove 3rd row if fitted
2. remove rear quarter panels, disconnect any courtesy lights if fitted, panels pull toward the centerline of the van
3. remove 3rd row seatbelts, and upper quarter covers
4. remove hooks from headliner (pry cover toward center, then rotate 90 degrees to remove)
5. drop front headliner (instructions in prior post)
6. remove trees from rear headliner, takes pretty hard pull, use panel tool carefully
7. remove dome light
8. Work headliner out from side and rear gaskets, try NOT to remove these, there is a very tenacious sealant that will get on everything if they are removed.
9. Drop headliner and pull out from van from rear. Note harnesses must be disconnected from front section when that is removed.
Once removed, the rails have 5 nuts, the center ones you will need very small socket on long extension to reach them through the airbags. You will also need to loosen the airbags brackets in the middle, flex it down and then you can reach another nut.
Generally, there are almost no screws holding the interior together, it all pops in/out BUT the trees and mounts are fragile and without a tool they are easily broken during removal. A very bright shop light is helpful, the front area of the van has very deep gaps between the floor liner, seats etc and if a stray screw goes down there it's pretty much gone. Keep in mind when removing the front shelf which has small screws deep in mounts....