I have always found dwarf gouramis to be aggressive towards each other, I have always ended up with just 1 and usually the female (I guess that is just my luck)
They are not particually aggressive fish, and they cant inflict much damage but they do harras each other and I have usually ended up with one getting wounds and dieing.
however they are cheap and it might work, its certainly worth a try.
can I also suggest you add some cabomba to your tanbk for them to eat and hide in, I always found they love it