"I can't prefer the baby over the dogs because it is not fair"
Yes, it's very very fair! I love animals, but when you decide to become a Mom, your children come first.
Now, about pitbulls. The fact is, if you're asking the question, I suspect you already know the answer. Pitbulls are a breed that is known for random, often unexpected, vicious attacks. Yes, the dogs love you, but as you said yourself they become agressive when you're around and with each other. How do you think they'll react to a baby that's occupying most of your time?
I wouldn't risk it, your baby's well being and possibly his/her life could be at risk. On top of that, if your dogs do attack, they'll end up put down anyways, so you're not really doing them a favor. Find them a good home somewhere where there are no children.
I know this may not be what you want to hear, but it's the only advice I can give.