But I read in Understanding Your Dog for Dummies that if your dog is snarling, and its mouth is in a "C" shape, that means it's dominance aggression. If it's pulled back, it's fear aggression. Checkers snarls in a "C" shape.
Nothing in aggression is ever that black and white. What you read is useful information, but it's extremely limited. Aggression and reactivity are almost never quite that simple. When a dog is growling, you're not looking at what letter their mouth makes. You're not looking at the teeth. You're looking at its lips. Are the lips pulled back or are the lips pushed forward into a pucker? You look at its front. Is the dog putting weight on the front legs or is the weight on the back legs? You look at its rear. Is it shifting weight on its haunches or is it tense and ready to spring forward? It's not just the ears, teeth, and tail you're looking at. You're assessing the entire body and the dog's mental/behavioral history. The differences are incredibly minute and an inexperienced person isn't often able to differentiate the physical subtleties. I myself often have difficulty differentiating the subtleties. I usually need a video camera to really precisely see it.

To be brutally honest, you *need* a behaviorist. Because you have so many dogs and are experiencing so much difficulty with at least 3 of them, you really should contact a professional. A behaviorist will help you decipher dog behavior and help you take back control.
Check this out: http://www.dogscoutsphilippines.com/
He is a positive reinforcement/pro-clicker guy, at least from what I can see. Please contact him.