Cortlens :
Yeah the video looks great, but the 76% pecent are nonetheless realistic. Of course we show only that parts that are finished and work correctly in such a video
In Duel-mode you can only take pistols and the knife if you are out of ammo. Reason should be clear. Or have you ever seen two guys facing each other, ready for a duel, and one of them has a big rifle ? He'd be dead before he'd be able to draw his rifle. That's simply a matter of realism. A rifle on the back takes longer to draw then your pistol at your side.
As Spoon said, the akimbo pistols are totaly independent. You can combine the pistols you want, and fire them independent. Left mouse-button for left pistol and the right button fpr the right pistol.