I have one male and two female blue throat triggers in a 180 gal tank. I started with the male then added the females about a month later. I was prepared before I started this may not work, that is why I put the male in first. If I had to chose I wanted a male instead of a female. They have been togther for around three months now with no problems.
I also have a pineapple trigger, it is his tank and always will be, and a mexican dragon eel in the tank. In my opinion four triggers (even mellower ones) in a 180 gal is pushing it. I have already started setting up a custom 375 gal (8' x 30" x 30").