If you have a big enough fuge you can try putting all your damsels in the fuge for a few days then move them all back to the main tank (also rearrange your main tank) and they will reestablish territories and maybe stop picking on the new guy. I just recently had to do that because my clownfish were beating up my new tang, I put the clownfish in jail (fuge) for a few days then moved them back, and now all the fish get along nicely.