They'll be fine, especially if you run carbon. I have two huge green BTA's right next to my gigantic RBTA in my 155 and all three have been fine with one another for over a year. I also have a mini carpet anemone in this tank. In my 40, I had two green BTA's next to each other and a Haitian pink tip on the other side of the tank with no issues. I've even done a baby BTA and a Haitain in my 14G. Of course, I've always ran carbon and done weekly, or at least bi weekly water changes.