Try to get the barons close to each other and then get one of 'em to blow up a barrel in front of 'em.
You should warp straight to E1M8, and there's no way you could win this with pistol, you need to do the trick explained above. It can take a while and a lot of tries to finish this, but it can be done. And don't shoot the barons! Don't even blow up the barrels yourself, or it will be much harder!
Id software, some guys at DoomWorld forums whose experiences of weird things in doom gave me the idea.