Still haven't specified which clowns they are though, which could make all the difference in this situation. It could just be that they are showing the new fish what the pecking order is, meaning who gets to eat first and what territory they own which usually happens for the more mildly aggressive clownfish such as percs and ocellaris. OR, it could just be flat out aggression aimed to kill the new tank mate, which usually happens with much more aggressive clowns like Tomato clowns.
Glad that rearranging some things helped though.
Another tip; turning off the lights for 10-15 minutes will also stop the fighting.