Well,unless you can catch the small one and out it in a breeder net and seperate them,they'll fight.
Usually they'll stop one the large one wins and becomes the female.
Could it be the ich causing the frayed fins?
Do you see the larger clown pick on the smaller?
If your clown has ich,they will all have it eventually,if not already.
The strees of the sex battle may have made the ich get the upper hand on the little guy.
The only way to get rid of ich is to treat all the fish in a hospital tank and leave the display tank fishless for 6-8 weeks.
There's no need to panick about it,just make sure it's ich first.Then do some searches on how to cure it.