I agree, having 2 pups together can be a problem.
Another thing you can try:

Remove all toys and bones from the yard when you
are not home.
(anything they could possibly fight over)
See if that works.
Of course their is no guarrentees, since dogs
can find even a twig to fight about.

If not wait till they are older than remove all toys
and bones etc. and leave them together and see
what happens.

I had to separate my dogs for 6 months, when
Rocky was a adolecent (sp)
He was getting into fights with Sheba.
(I also removed anything from the yard they
could fight over.)

Once he matured, I still kept the yard free from toys
and bones but was able to leave them together when
I was not home.

They haven't had a fight in 3 years now.