Your best bet is to get a positive reinforcement behaviorist to come in and do an in-home visit. Only a person who is there IN PERSON can determine what type of aggression you are dealing with. Dogs give very, very subtle signals that show which type of aggression they are feeling, and what you do to help one type of aggression will feed the other.
Look for a true animal behaviorist that has a Master's Degree. Some people "claim" to be behaviorists but have no degree at all. A very good professional trainer can be of help too.
Avoid all punishment based trainers as that will only cause the dog to shut down and stuff the aggression. With both dogs living in the same household, the aggression will then pop at some point - and violently. You can see the video I posted of "punishment based" training.
There are some hubs here on aggression. I recommend reading some of http://hubpages.com/@alexadry hubs. She has some good behavior hubs. I bet Dr. Mark does too.
But nothing - and I do mean nothing - is as important as face-to-face evaluation when it comes to aggression. As a professional trainer myself, I would never consult on aggression on the internet or over the phone. You have to see the family - furred and smooth - in action in the home environment.