From my experience, if the clowns have an anemone/territory that is out of site of other clowns you will probably be fine. I have a 125 with a pair of A percula in a ritteri, a single A sandaracinos in a haddon's carpet, a single pink skunk in a LTA and a recently added pair of b/w A occelaris in a ritteri. The anemones are spread over the tank so that they are each minimally visible to one another. The two ritt's were closer together before I added the b/w clowns. As soon as the perc pair saw another pair of clowns in it they moved in and evicted the new clowns. I had to rearrange the tank slightly to block the view between anemones, and now things are peaceful again. No guarantee it will work for the long term, but it is working well for now.
If you don't have clearly defined territories for the clowns. I would not recommend it. But it could work out OK, especially in a large tank. There have been numerous threads on this subject, with many short term success stories. good luck.