I was told you should always try to get clowns that are raised in the same tank so there wont be a problem!
I guess you cloud put them together and if they start to thrash each other, you'll have to remove one.
I have seen a clown violently beating another one (maroons) and it was a very sad site!
It was in a pet store and I had to tell the workers to remove the one being beat up.
the poor little guy was on the suface of the water gasping for air and all his fins were tore up!
The "beater" was chasing it around no matter where it went and was biting and beating it up. And this was in a 55 gallon tank!
Very violent and very sad.