Declaring a dog as dangerous for attacking livestock is wrong IMO. You, the owner or your brother if he was supposed to be in control of the dogs should have to pay compensation to the owner of the livestock and should also cop a pretty hefty fine. Declaring it as dangerous is just ludicrous in my mind. Having said that, I doubt you'll get much joy in the courts, unless maybe you get a very good lawyer and go all the way to the supreme court which will end up costing you 10's of thousands. A horrible situation for you and your dog and one I certainly hope I'm never in.