Tweaked yes. "Can we get Varric/Iron Bull to kill a qunari/dwarf?" doesn't sound like a tweak. Being realistic.
Err... Not sure what you think the problem is. Lots of death scenes don't involve any interaction between models. Remember the scene where Varric killed a blood mage apprentice?: One second the man was talking, then we see a crossbow bolt hit him, then we get a shot of Varric holding the crossbow.
IB would be a shot of the person, a shot of IB swinging his weapon and blood splattering, and then a shot of them falling lifeless to the ground.
I think it's more relevant that you need two animation for each of them as they can be equipped with different weapons (crossbow/dagger, 2-hander/sword and shield).
I'll also say that this thread has sort of dramatically overstated the difficulties of including dwarves and qunari in romance scenes. It's an extra cost, yes. It's more difficult than the default of elves and human, yes. But it's not some incredibly difficult, hair-pulling exercise.
Look at the ME 3 Liara romance scene. There's Shepard sitting on the bed, they touch hands, Liara undresses and the camera spends time panning over her body, and then Liara leans over Shepard in bed. If you changes that to a qunari and dwarf making love, you'd need to do some tweeking, but the original blocking is such that height differences between participants aren't a big deal.