Your clowns may or may not host the nem,they're finicky to say the least but always curious. I would just keep an eye on it. The clowns take time to establish sex and hiearchy so the fin nipping is a part of that. I have seen clowns go after each other and when they are set on driving someone out they are very relentless driving the weaker right to the top of the tank, but it goes way beyond fin nipping. Just let nature run its course. I'm sure some others will be of more help on the nem. Welcome to the reef!