You have two pairs of zebra finches and the two females are fighting what can you do to stop them from fighting?

The females may want to establish nests; for two pairs (2 males and 2 females) you should provide three nests so they don't have to fight. Also, the males will try to mate with both females if they can, this can also cause fighting.

One time one of my females had eggs and the other didn't. The one that didn't have her own eggs wanted to sit on the eggs belonging to the first one. That caused fighting, but it was OK for the other male to sit on the eggs!

If the cage is too small for so many birds you should separate them.