Your father is Type II diabetic for last 7-8 years, Uncontrolled as 620 mg% what sample is this,I mean Fasting,Post meal or Random Blood sugar in any case if it is correct this is very high.
Is he Obese and having BP or heart disease
Diabetics are at risk of complication known as Keto acidosis albeit rare.
You these patients are having insulin resistence hence insulin sensitizer like Piglitazone and metformin
are used ,But You are in Mumbai in our country people are very reluctant to take Insulin injection hence a higher dose of these drugs is used .
Ideal treatment would be a Metformin and Long and Short acting Insulin
Healthy Diabetic diet ang regular walking once he improves for control of Diabetes
you may hospitalize him.
Consult a Endocrinologist/ Physician have a complete medical checkup
All the Best hope he agrees to take Insulin.