I'm so sorry you're going through this. There is nothing worse than an aggressive dog that you have no idea why he's like that.
My question: I think one of your posts said neither the Rott or Yorkie were "fixed". That might be the problem.
I also thought you said the Rott was an outside dog? How did your inside Yorkie take a bone or toy away?? Did the Rott come in when he saw the Yorkie get the toys?
Maybe take him to a long term away from home trainer. Then he can come home "fixed" and better trained.
I really hope you find a way to help them. So sorry