There are two types of treatment options.
First, there are the pharmaceuticals and dietary/supplement measures to reduce blood pressure. Although these only address the symptom and not the cause, they are important because high blood pressure, itself, causes other damage. Without any expert knowledge on this aspect of it, I would probably take the pills prescribed by the doctors. As far as diet/supplements go, beets are pretty good. Roibos/hibiscus teas help too. Melatonin helps with nighttime blood pressure. Eating a low sodium diet may also help and should be tried.
Second, there are dietary measures and supplements that can help fix the underlying metabolic problems that lead to high blood pressure, in particular, and that lead to cardiovascular disease, in general. These include generally eating a nutrient dense diet (i.e., skip the bread, sugar, alcohol and oils -- and processed foods of any kind). Avoiding processed foods pretty much makes it very easy to avoid excess sodium too. The starting place for healthy eating is consuming only whole foods (i.e., nothing that comes in a wrapper). It makes sense to go further, however, given your dad's state -- it also makes sense to limit omega 6 oils (Avoid: vegetable/nut/seed oils. Limit: nuts & seeds, pork and poultry fat, avocados, eggs) and get enough omega 3 fat (2-3 servings of WILD salmon per week is sufficient; flax seeds are also good for those that strictly limit omega 6; grass fed dairy/beef/eggs should be sought, if possible). Get plenty of minerals from diet also. If your dad has good glucose tolerance (i.e., not pre-diabetic or diabetic) get your carbs from potatoes and other mineral-rich root vegetables. If your dad is pre/diabetic (which he probably is), get carbs from WHOLE grains (i.e., do NOT follow the paleo diet here), with primary emphasis on irish cut oats, real whole buckwheat, and wild rice (probably still good to avoid wheat). Eat a moderately HIGH fat diet (30-50% of calories), with serious emphasis on the more saturated fats (i.e., strictly limit polyunsaturated fats - to about 4% of calories). Take enough vit D to get levels to about 40-50 ng/ml. Take a low-dose vitamin K2 every day. Take a low-dose (perhaps a quarter of the recommended dose) multi-mineral (without iron) every day. Perhaps also add an additional low-dose supplemental magnesium.