My dad is 78 has 2 blocked arteries and another that is 80 blocked his heart is working at 20%. What are his options?

Maybe ICD. In addition to medication, possible catheterization, angioplasty, or bypass, would also consider adding implantable defibrallator to list due to 20% ef.
CAD. Your dad has significant coronary artery disease and should be on appropriate diet, exercise, not smoking and polymedicine treatment. Depending on his other factors he might benefit from bypass or catheter based therapy if appropriate. His options should be discussed with his doc/cardiologist.