Clownfish are colonial by nature. If the new fish are juveniles they will be accepted by the pr and allowed to be part of the colony. Then if there is appropriate space, the newer fish may pr off and choose their own space within the tank, if there isn't enough space, they will remain part of the colony.
Once they have paired and found their own space, there may be territorial disputes, but usually nothing too serious.
If they fight when added, this may mean they are not juveniles and have already started to transition. Even in these cases, as long as one of them hasn't made it all the way to female, they will usually still coexist.
I have also found that for about every 2' of tank length a pr of ocellaris/perculas can coexist. This is a generality, there are exceptions, but for the most part works out.