If two females see each other they will [B]fight[/B]. As long as something that block the view of the clowns, in a 8 foot tank, you can have three pairs if you have natural hosts for them. This wil keep the clowns from wander and run into each other.
I am only experienced with smaller docile species namely Pink Skunk, Ocellaris and Percula. These three species will never wander more than an few inches from tehir anemones, especially if you have large fishes in the tank. My tangs are large, I also heve a Harlequin Tusk which, I am sure, are very intimidating for the clowns.