Gourmais can be territorial and downright mean to thier other gourmai tankmates. I would keep the one you like the most as a centerpiece fish and return the rest of the gourmais. I have the same size tank and IME only one gourmai prevails in a tank that size. Other tankmates are fine with the gourmai as long as they are not in the same family as the gourmai.
Marinemom
Marinemom