I'm sure there's still some "pecking order" probably going on, and you have to let a certain amount of that happen on it's own. But when the barking goes beyond that you need to step in. You need to get their attention focused on you before you tell them no. If they are still focusing on each other, you can talk till your blue in the face it won't make any difference. With my two, usually a quick firm touch on the neck will break their focus and then I tell them quit. If that doesn't work, usually Gracie will be the one to continue barking, another more firmer (
such grammar!) touch and again the command, Quit. If that doesn't work, sigh and sometimes it doesn't with the little Princess
, then I pick her up and get her right in my face, growling the Quit to her. This nearly always gets her attention PDQ. She may try to start up again when I put her down, but now the touch and command will work to get her stopped. It's the puppy in her, she too is the bully of the pair, but it's getting better each day.
Mainly tho, you have to change their focus from each other to you. I'm sure you will have many other suggestions, just try them and find the one that works for your girls. Good luck!