Don't know if you ever heard about this, but you could use something called "oil eater". We use it for many things around the house, even for the laundry. It works well for stains of all sorts, just make sure to mix properly. Hope this helps, good luck.
I would use sponges with degreaser on it. Or use wipes. There are books on how to clean practically anything. But, it still depends on the type of wall it is. You might have to repaint if you still have some stains left.
It would depend on the type of paint that is on the wall. Flat paint is porous and will absorb the color in the spaghetti sauce. You would have to scrub the sauce from the wall with a household cleaner, then re-paint to cover the stain which would be left behind. If the walls are painted with a satin or semi-gloss paint, you can most likely scrub it off with an ordinary cleaner, but it may still leave a stain. If you use nailvarnish remover, you will take the paint off the wall. Turpentine would probably be okay to try. Getting red and orange stains off of anything is very difficult, so there's a good chance you will have to repaint once you have scrubbed the spaghetti residue off. ♀
