modern drywall is a layer of grey cardboard over white powdery rock, gypsum. in the olden days drywall was tan cardboard over gypsum. do you know that the walls are actually drywall, if the house was built before WW2 it may have plaster walls.
your top layer sounds like vinyl-based wallpaper. i'd pick a small area and soak the heck out of it with water and keep carefully excavating til you know what you got.
if you have many layers, a steamer might be helpful, i've gotten 6 layers off at a time but had to hold the steamer in place for about a minute, this was on plaster though - plaster you can do this with because when you get through all the wallpaper you have that nice smooth rocklike surface. on drywall when you get thru all the layers, you have...cardboard.