Hello and thanks for the query
Firstly I want to know some history like weight, physical activity, Hypertension
, Diabetic or other orthopedic problems like PIVD etc. Cause of pain lot depends on this.
As per your mail pain reduces by antihypertensive drug, so needs to be investigated for this. If he has swelling in feet than do for Echocardiography
and consult your doctor for further treatment. your father may need diuretics for this.
Other possibilities for back and legs pain may be PIVD, go for X-ray LS spine and rule out this.
You also needs urine culture examination and investigated for OSA symdrome for night sweating.
Hope you got answer to all your queries.