So narative is that my two weapon fighters always swings his heavier weapon and misses and then swings his lighter weapon and hits. Then if he rolls enough advantage he activates his heavier weapon to continue its fluid motion and hitsee on the back swing motion. Now it's realistic and fits game mechanic
That's how I've been playing it with my Niman who uses Shoto as primary and standard lightsaber as secondary. Works well enough.