I don't think you can rely on ANY effective handgun round to not penetrate two layers of drywall and thus hurt someone on the other side. If that is what your walls are, you are going to have to make some very careful plans about how to handle home defense or choose a non-firearm type of weapon. I live in an old apartment and have the same problem with not just the walls, but the ceiling as well. Think it through and establish procedures for yourself and your family.