Thanks for the remarks. I have been a multiple dog owner for over 25 years. I asked a question and get downed for asking. This is definitely not the board for me. If there is a way that I do not see to delete this thread please do.
I'm confused. What do you mean that your dogs have always been aggressive to other dogs? If they can interact with a new dog at all, it doesn't sound like they're dog aggressive, but if it's a concern why add another dog before getting to the bottom of their current issues?
I would start with working on the dogs you do have. Take them out one at a time and work on basic obedience, so they are under control when out and about. Once both/all of them are at that point, starting taking both of them out, same idea. Then the third/forth (not sure how many you have). They do not have to 'like' every dog they see but do not need to be rude either - to me that means that when they see another dog across the street, they should be able to see the dog and perhaps watch to know where that dog is, but not growl/lunge/bark out of control at them.
Then when they are able to do that, have the new dog walked at a distance, first in front, then beside, then eventually closer so that she's side by side with your other dogs - or do that one at a time with the other dogs.
To bring a new dog into the house, what I have done with rescues is I bring the new dog in but the others are crated or behind a pen, and everybody rotates for a day or two, then I start with one of my guys (depends on the new dog as to who that is) and so on. But I do have contol on my guys so I can say 'enough' and they'll settle if there's any snarking. This has worked with questionable dogs that have come for fostering/training.