M.R.
He should not be taking supplements unless a medical professional, who knows his health history and recent problems, instructs him to do so. Stop the magnesium, vitamin E, and St. John's Wort - is his mom and the "someone he heard from" a doctor or other medical professional?
If you don't fancy western medicine that's fine but don't start popping every homeopathic pill just because someone said it was good. Get advice from a nutritionist, doctor, nurse, dietitian, etc. The blood pressure medication is probably the most important medicine he is taking and you do not want the others to interfere with that.
Also look into the DASH Diet. You can Google it. It is the Dietary Approaches to Stopping Hypertension eating plan that can be followed for a lifetime. It includes natural foods that are full of bioavailable vitamins and nutrients (and our body likes those better anyway) that will not only help his blood pressure but improve his overall health.