Editing The Great Commorragh Campaign Rules (section)

===Paired Weapons===
Using two weapons gives you +2 to your Parry and you may choose to use both special effects of your weapons by making all rolls with the lower of the two skills. Wyches have access to the Wych Weapons skill which combines two skills and so they get no penalty when using those, and anyone may use identical weapons at full skill since there is no extra special ability to gain. 

Paired knives gain +1d6 damage (negating their normal penalty) so they are slightly less effective than a sword.