Rules as written you can attack the same enemy multiple times even without the 'Dual Wield' talent. In the 2.1 version of the rules neither in the section for multiactions nor multiattacks does the text explicitly say that the actions/attacks you declare have to be different actions/attacks.
But reading through the examples given after these sections however, I do not think that this is the intention. And at higeher tiers of play this would allow characters with high damage dealing weapons to trivially one shot any target.
So if you go with the interpretaion that each attack you make has to be distinct, then it would allow you to attack the same target twice. Once with your left and once with your right. Using to diffrent wapons makes this even clearer. You could be wielding a pistol and a sword. Thus making a melee attack and a ranged attack. Two very different actions. Wielding the same weapon twice should not suddenly forbid this.
Mobs can always be multiattacked as per this paragraph:
Mobs & Multi-Attack
You can use the Multi-Attack to target multiple
individuals of your choice in a Mob. When you Test to
hit as part of a Multi-Attack against a Mob, each Icon
over the target’s Defence means you hit an additional
target in the Mob, as normal.
When using a melee weapon you could potentially kill so many troops of the mob with the first attack, that the mob is no longer in range for additional attacks. Though if you still had movement left you could then followup for further attacks.