Dedalus would attack people if he got drunk enough. Honestly? Having him in an all out duel would be hysterical, because... well... he'd probably give up halfway through and try to start fist fighting the person.
Severus honestly doesn't have the stomach for much retaliation. He'll make it look good, of course, but he's slowly starting to come to the realization that he made the wrong choice. Very, very slowly.
Barty just wants to torture things, blow shit up, and kill people, sooooo.... he's up for anything! What with being stuck in Hogwarts, though, it would probably be difficult for him to get attacked. I could definitely see him sneaking out and helping with a coordinated DE attack, though.