I have to install the left, staircase wall. It must be wallpaper before installation because it will not be accessible afterwards. This wall will enclose your staircase and you will not longer have access to it so do your touch ups now.
You must prime the wall and mark, by dry fitting the wall, where the foyer is located so you can use the right wallpaper. Wallpaper the foyer area on the wall.
As you can see, this is why using a bordered wallpaper in the foyer is not recommended. I have to find a way to make sure that the borders line up at the corners and this will be very difficult to do when I have to wallpaper a wall away from the others. But, this wallpaper is already up and is staying so now I just have to problem solve.
While your wallpaper is drying on the staircase wall, take some time to inspect your foyer and staircase again. Do any needed touch ups. At the top, where the staircases top riser meets with the doll houses second floor, there might be a gap and it can be hidden with spackle.
I went ahead and applied the ceiling paper to the foyer. The ceiling paper is applied around the staircase and must be done now because the ceiling will be inaccessible after the staircase wall is in place.
Fry fit your wall and make sure that the slots for the staircase wall are large and will not be a problem. Sand them down with a fingernail file and in extreme cases, use a flat head screwdriver to twist in them so the slots are large. You don't want to struggle with this wall when it's time to install it. Use your mallet to fit the wall. Dry fitting it first to get a feel of what's the easiest way to install it, will help. Apply glue to the wall but be careful with your wallpaper. Wood glue can not be used on this wall. It will stain your wallpaper.
After the wall is installed, you might be able to see the joints between the walls and this can look bad. Cut a strip of wallpaper, fold it in half and glue it to the joints in order to hide them. You will have a hard time reaching in but fixing these visible joints will be worth it.
Notice that I haven't installed the second floor railing yet. You can not install this railing until you wallpaper the second floor stairwell, which can't be done just yet.
Inspect, touch up and clamp. Let this dry overnight.
