I have one haddoni and one gigantea in a 120. The gigantea was added 8 months ago. It was bleached when I got it. It's color has greatly improved, but it has lost mass. Probably because it was bleached. It eats well, and seems to be gaining mass again. The haddoni is its normal, snail eating, self.
I am a firm believer in chemical warfare between anemones. It seems to be working out in my system between these two species, but that doesn't mean it will work in yours. I do run a lot of carbon and I do large water changes.
There was one odd thing. My haddoni had not moved in years. The day I added the gigantea, the haddoni took off. Within hours, the haddoni was right next to the gigantea. Almost touching. I moved the haddoni back, and he hasn't moved again??????