[MasterNuke]

You could probably classify dual Tomahawks as a two-handed weapon... have them attack like any other weapon except the animation shows it swinging both tomahawks and the damage be dealt twice kind of like how the naginata's spin animation has two attacks in it.

To prevent a shield being equipped with it... I guess they could script a flag that could look like this "(no shield)"

But... if you're thinking that one weapon in one hand and another in the shield slot (off hand)... then we need to think of some dual-weilding mechanics.