Try ti use Macconkey or Baired Parker agar media to eliminate Bacillus growth, but if the problem persist add Vancomycin. Staph.auteus is resistant, however Bacillus will die
It is possible to separate them using the selective media. First grow it in the MacConkey broth for 2days(Enrichment) then streak it on MacConkey agar plates. After incubation you should get good growth of red colonies of S. aureus culture.