Re: What kind of walls are these?
If the "particle board" is straw-colored, then you have celotex. If it's darker brown, it's beaverboard, which is worse. Celotex with three coats of plaster was used for walls and ceilings around the 30's in my area. It's somewhat satisfactory on the walls, but a real fiasco on ceilings, as it sags and sags. Never seen beaverboard w/three coat plaster on it, but it's another depression-era economizing move to find a cheaper wall material. Beaverboard was made from processed agricultural byproducts, not beavers ;-)
Remove not the ancient landmark, which your fathers have set.