Meaning of the Sanskrit Word: pitrbhih

  pitrbhih—by the forefathers, the father and grandfather    SB 4.8.37
  pitrbhih—along with the residents of Pitrloka    SB 1.15.49
  pitrbhih—by the Pitas    SB 4.6.8
  pitrbhih—with your forefathers    SB 7.10.18
  pitrbhih—by forefathers    SB 4.12.26
  pitrbhih—by the parental guardians    SB 1.12.31

Can't find any compound Sanskrit words containing pitrbhih.