My intact male yorkie has shown some possessiveness and a few bursts of aggression toward our rescue, Finn, so I've been reading up on reasons for various incidents. I've figured out the body language a little better and discovered that, usually, Keegan has misinterpreted something Finn did/is doing (Finn is oblivious and focused only on pleasing humans). Also, the energy he picks up--frenzied, playful puppy Piper can add to his agitation if he's feeling threatened and increase the likelihood of accidental outbursts.
The ASPCA site has some good info, although I'm not sure if it will be helpful for your situation. I hope you and the pups get it worked out, though.
Aggression in Dogs | ASPCA