Sword + Shield Beats Sword + Sword

 When facing sword+sword with weapon+shield, ironically the shield becomes your main weapon. 

 

 Sword beats unarmed.

 Two swords beats one sword. Engage their weapon with one of yours, then stab with the other weapon.
 You can sometimes simply slice with both swords, and they'll only be able to parry one. Unfortunately if they're smart and know they can't win but don't run away, you invite a suicide attack. Best to ensure the parry while going for the stab. 

 There's a good reason not to wear shields around town. They're inconvenient. Heavy, bulky, in the way. Same reason you don't casually walk with a spear. Presumably there was a good reason not to wear two swords around town, but I have no idea what it might be. I mean, I understand samurai did wear two swords around town.

 Sword and shield beats two swords. Engage their weapon with yours, then shield bash. Your shield can attack and defend at the same time.
 If they're trying to attack with their other weapon, try to break their wrist. If they're trying to defend, you can try to shove their weapon into their own body. If they try to pull back from your shield, shield-check them. Regardless of what they're doing with the main hand, you can lash out towards it with your shield, both blocking the weapon and slamming a big heavy shield into them. They will probably realize they're losing and run, but if they don't, keep at it until you've done enough damage to make them drop the weapon. Whereupon it's like two-sword vs. one sword. Set up a block and go for the stab at the same time. Checkmate.