How to treat high blood pressure whilst battling diabetes and cancer?

My father has high blood pressure which is caused by his cancer (since it has become metastatic the tumors cause it to elevate even after administering medication, which then requires going to the ER). The problem is that his blood pressure gets extremely high but his sodium levels are very low due to his diabetes (he sweats it out). He has many doctors which treat him for various problems and they all have their own opinions as to how to treat it which can be contradictory with what his other doctors say. His last visit to the ER (yesterday) his doctor who treats him for high blood pressure ordered an IV with sodium chloride. A few weeks ago his blood sugar dropped to 32 which had a serious effects on his brain causing him to hallucinate and be out of touch with reality. Luckily hes not in a coma which is what happens with situations like this, but unfortunately the damage done to his brain is permanent. My question is, how do we treat high blood pressure when his sodium levels are very low?