After a fight follow the dogs to see if they are protecting something, or they don't want to have pups, not to upset anyone.

 Hopefully you can link the aggression to a behavior or event.  Is there a toy or food involved?  Does it happen when you are giving attention to one of the dogs?  Is there a person or object they are protecting?
Contact a trainer or behaviorist who will come to your house, assess the dogs and the environment and develop a behavior modification plan.  To correct negative behaviors both behavior modification and behavior medication needs to be done.
For now these dogs need to be kept separate at all times.  Interactions together need to be short and well supervised.  A basket muzzle can be used so they are not able to bite each other if a fight starts.
This needs to be addressed immediately as aggression tends to escalate.  People may get injured while breaking up the fight and the aggression can become redirected to people.