Major update:
As soon as I finished doing the first coat on the 2nd wall, I noticed some wallpaper peeling off, just like cdaniels mentioned.
I started to peel the wallpaper off, and it came off really easy!!!
I got 1/2 the first wall done, then I noticed a different pattern on the wall (a brown layer, not sure if part of wall or not). This confirms my theory that the house was "extended" before I bought it... (1/2 the room has hardwood subfloor and 1/2 has plywood subfloor).
I didn't have time to finish it all, but I took some pictures... Few questions:
1- What is the "brown layer"? Is it glue or something part of the wallpaper? Does it have to come off or can I paint/prime/skim coat on top of it?
2- What do I do now?? Some of the brown layer comes off easily, but some is really stuck there.
3- What would be the process to get the walls going again? - Skim coat + prime + paint?
Any suggestions/comments are appreciated.. I'm lost again
EDIT1: Picture 4 shows the difference between the "brown layer" and the plaster wall (
AFAIK).
EDIT2: Picture 1 = ALL wallpaper has been removed.. it shows how the wall has 2 different textures/material.... 1/2 is either new plaster/drywall and 1/2 is clearly plaster...