Yeah, sad to say I have this bug too. I didn't know if it was possible to shoot them down, but I tried the same as you did and all that happened was the targetable area disappeared.
Instead,
I went into hiding and dragged over some barrels strategically
to help me.
This...
I placed a load of barrels around Dror and his minions. Then climbed up onto the rafters and threw a potato at the pice of wood holding a brazier.
That's another big incoherence in the game. Just for fun I decided to use the barrels so I wen aroun picked them, place quite a lot near the boss and his followers and then killed them with one blast. I wonder why the boss or his underlings didn't say anything. Come one there is people placing dangerous ecplosive stuff near you and you don't flinch even a bit? [On the other side it was amazing the fire work
]
