If I were a betting man, I'd say in a similar style to the Devil May Cry games. They can hit things at a distance, but do damage that even when upgraded, is fairly pitiful compared to actually going in and twatting something with a large metal object. So they end up being more of a situational weapon than a primary one.
As for dodging, I think animations would be key. A flintlock-pistol for example, isn't something you can fire subtly from the hip, so a noticeable firing animation that you can time your dodge to would potentially work.
Early firearms were also notoriously inaccurate and given the Souls-series' penchant for fairly realistic combat, I can imagine another way of doing things would be to replicate that approach instead.