As your father has undergone a treatment recently in the hospital it looks like he has aquired a hospital aquired pneumonia
. These bugs from the hospital can be multi drug resistant and hence not much of antibiotic options are vailable for them. However i m sure they must have taken some sputum or tracheal culture and got the bug identified along with the antibiotic options available.
There are many good chest physicians and infectious disease specialist practicing in delhi NCR region and they can help you out on that.
Drugs like sulbactum in a high dose or clistin
or high dose meropenem