Your dad's doctor knows what is best for him...we couldn't possibly, as anonymous people on an internet forum, tell you what is needed for optiumum health.
I will say this though: It often takes 2 or 3 meds in combination to bring high blood pressure under control. This is quite common.
As far as losing weight, he should aim for a diet high in vegetables (especially dark, green ones) fresh fruits (berries are the best) and lean poultry and fish. Red meat is high in saturated fats and should only be eaten once in a great while, and then only in small quantities (4 ounces or less...about the size of the palm of your hand.)
Anyone with diabetes should avoid alcohol, sugary drinks (soda, juices) processed foods, sugary snacks, baked goods, white flour, white pasta, chips, crackers, etc.
Hope this helps!