Well I may be wrong but I think the female in a pair of clownfish is dominate and very territorial. If you do get two types of clowns (I wouldn't do 3 or more), try to acclimate them to oppisite sides of the tank. If you're getting an anemone put those on the oppisite sides so both pairs will stay close to the anemone on oppisite sides. Also I wouldn't try a maroon clownfish and another species because Maroon clownfishes are more aggresive. What types of clowns do you have in mind?