Gouramis can be quite territorial, and one will usually dominate a tank. If the others aren't given refuge, they'll probably be endlessly harassed. Here's what you can do to help all your gouramis coexist without too much stress:
Switch around the territory markers. If they weren't all added at once, it's kinda unfair to introduce a new fish into a tank when another of the same type has already staked out territory. They'll be chased around before they can even get their bearings. Switching around tank decorations forces them to choose new spots and may give the new fish a better chance at holding down a territory.
Divy up the tank with caves, loads of plants, and decorations. If they are in a smaller tank, but can feel secure, then they won't be stressed out. Give them places to hide, so that if they're ever being harassed too much, they have a place to get away from the others.
Other fish in the tank may help, but it's no guarantee. Tetras and rasboras may distract the gouramis from each other, but may create new problems... Have a backup tank in case they get harassed nonstop as well.
You could try trading in males for females, if your LFS has any. Gouramis won't peck and chase females as much as males.
Best of luck. I love my gouramis, but they are little delinquents, and they will have scuffles now and again. Someone made a good analogy- it's like brothers fighting, mostly it's all scuffles here and there, no harm done, but you gotta keep a close watch on em.
