So if most swords are one handed, why not allow you to have two swords at once? (I assume you can quip two pistols at once, if not I suggest that also). Rather than giving the individual actions, have two actions set for 2 x pistols and 2 x swords.
Example of two swords attacks.
Left click - Swipes swords in front of him 90 degree arc
Right click - Spins around swords extended so clears space around him.
Left click - Slower more accurate fire from both pistols straight out in front
Right click - Faster rate, but less accurate fire that causes more damage?
Or possibly with two pistols get specialist ammunition?/ Combie weapons (E.g bolter with flamer/melta attachment)