The first thing that you must always remember is that this is NORMAL behavior. Dogs will fight over status and will continue to fight until it has been established. It seems to be worse among females with the fights generally being more aggressive. I am sending you several links on this that will help explain it further and should help you make some sense of it.
DO NOT attempt to break them up by stepping in between them, grabbing their collars or picking one of them up. This is something that should NEVER be done by you unless you have experience in handling aggressive dogs. You can use a water bottle or the hose to spray them with, a broom to distract them or a dog whistle to get their attention. There are several other ways described in the links I sent you as well.
I hope this helps. Please let me know if you need additional information.