They will kill the clowns, they were in the tank first and it is their tank now. In the end they will fight each other as well, and bite you if you put your hand in the tank.
There are fish that can go with them...I don't keep damsels, for the above reasons, so I don't know which ones.
If you want certain fish like, clowns, dottybacks, angelfish, or gobies...you must get rid of the damsels.