My neutered pointer was 5 and very spoiled when I brought him home a very unasked for 10 week old female pitty sister. My pointer was resource guarding and a bit nasty to the pup at times. She was intimidated but as other pit bull owners know she reacted by agressing rather than submitting.40 lbs of angry red head!
I had a trainer come consult and they were both put on the ‘nothing in life is free’ program and with lots of supervision and some maturing on my pit’s part they are now the best of friends. If they ate confident in their leader (hopefully you!) they are much less likely to duke it out with each other.
That being said I have been told that bitch on bitch agression like what your describing is the most difficult to deal with, and even with work you may need to accept these girls cannot be unsupervised together.
Get thee to a CPDT ASAP! I also really like the books written by Patricia McConnell, they are cheap, easy to understand and have their basis is applied behavior analysis and not dominance theory based on faulty research.