How can I use double lightsabers?
Yo get one about nearly half way on in the game, don't really want to spolie it but you lightsaber will get broke and yor have the choice of a new one.
At that point you can select the double saber instead if you choose...
In Multiplayer of course you just go into your character profile mid-game and change it. Respawn and you'll have your new weapon ready to go! ;)