I recently got Derkeethus the Argonian and he's pretty awesome, he'll dual-wield with his pickaxe and a normal weapon. Sometimes he'll even use two staffs, it's nice letting him summon creatures and shoot fireballs when he wants. Though he's not perfect, I was wondering if anyone knew of any followers who're more inclined to use dual weapons?

I looked online and didn't really find much, most lists only say what their primary skills are. Not behavioral patterns, or anything like that.

I gave Janessa 2 scimitar's and sure enough, she used them both for a long while, but for some reason she stopped after 20 hours into the game and refused to use both again, weird

Is dual-wielding possible for all of the companions??? I gave my Lydia a daedric and a ebony sword but he didn't use both of 'em but still used a stupid orcish shield and daedric sword.

You have to be careful what you give them. For example, the housecarls (Lydia, etc) will prefer a two-hander or sword+shield if their inventory allows for it, and so will lots of other characters.

I think Cicero comes with a pair of dual-wielded Ebony daggers, but I don't remember for sure.

Illia (darklight tower) would dual wield staves I gave her... she was awesome.