There are normally two options, bypass surgery and placing stents.
What the best option is for your father depends on many factors.
A few factors that I can think of are:
-your father's physique
-the skills and options the hospital can offer
-the exact position, number and extent of the blockages
-the impact of his diabetes on surgery
There are for sure much more factors that need to be taken into account for making a decision on preferred treatment.
His cardiologist has the knowledge and also knows the details on your fathers condition.
You really need to discuss the options with his cardiologist.