it is also possible for a firearm to doublefire. its most common with un maintained semi auto pistols, but can happen easily enough with large calibre revolvers, due to the recoil.

It doesn't have to be unmaintained. A 1911 pistol can be made to bump fire pretty easily, especially if you have it in a weird position. While it really isn't impossible, if you take kind of a Bayesian view, the likelihood that it was mis-attributed murder probably goes up considerably once you restrict yourself to the subset of double gunshot suicides.

By not dying after the first. It happens.