My apologies , I missed your previous post stating it was a 30 gal and was going by your "My Tank" that says 10 gal.
But , I agree with HN1 and I would rehome them .Adding to their shoal may not curb their nipping .Even though adding two to my serpae school has curbed their nipping , they still , every once in awhile , take pot shots at my Red-eyes or Danios . I do not have any long-finned fish other than a couple of my Danios , which the Serpae can not keep up with . So those long fins just may be to good of a target to pass up no matter how many Serpae you have in there .