I went through this in 1989. Had a large living room in 60 year old house with - count 'em - 8 layers of paper on walls and 3 on the ceiling. I tried everything and finally discovered that the key was water. I cleared the room and got a bucket of hot water and a sponge mop. Ran it up and down a section of wall and soaked as much water as I could into it. Sometimes whole areas would come down several layers at a time, Other areas were resistant, especially where the paint job was not bad.
This takes a lot of hours with a wide knife and a water bucket. When you are done the plaster will have plenty of pock marks, but I filled them and the age cracks with drywall compound and sanded, then painted. But it can be done.