Hello and thank you for using HCM. I carefully read your question and I understand your concern. I will try to give you my opinion about this problem and explain you somethings. When we treat hypertension our goal is to take mean blood pressure values below 140/90 mmHg and in a ischemic heart disease and diabetic person even lower. In case of your father If I was your treating doctor i will search for reasons that keeps the blood pressure high even taking different medicines as you say. It is essential to control his renal function. A diabetic person might have alterations of his renal functions that maintains his blood pressure high. My opinion is he should do some examinations like blood analyze, creatinin, a cardiac echo. If heart function is normal, if renal function is normal and if I was the treating doctor I should add to B-blockers some other medicine like ACE-Inhibitors like ramipril,enalapril ect. This are a very good class of medicament, very effective, especially in diabetic patients. Of course the dosage should be initiated with the smallest one and than they can be raised or add another class like diuretics or calcium-blocker. So, my opinion is you should not worry and discuss this alternatives with your treating doctor. Hope I was helpful. Best regards.