OK, so are you sure they are fighting, and not just loud talkers when they are playing? I have a puppy now and he just makes all kinds of noise when he is playing, it sounds like he is a vicious dog, but he is just playing. So if they are just playing leave them be. Now if they are really fighting, you need to figure out what they are fighting about, toy, food, attention, etc. Once you figure that out, maybe you can make it so that they don't have to fight over what ever it is, and they can each have their own, or something. Then you have to teach them that this is not acceptable behavior, you need to let them know that you do not appreciate them acting that way towards eachother. Whenever they are together and they are calm, or playing with eachother, praise, with a "good dogs" or something like that, and when they start fighting, distract them with something else, and as soon as they stop, praise, they may just be setting up their pack order, and it might just go away once they figure out who is the boss between them. Good luck with your pups
Make a loud clapping noise ever time they fight. Or beat on the bottom of a pan
Are they fighting, or are they playing? If they are fighting, I suggest you sell the agressive one. If they are playing, just leave them, they will grow out of it.