If possible keep them with you in bangalore.. Or you find a job in Delhi.
Rest all suggestions on calls, keep visiting often, checking is to cover the guilt..
If you really can't try solving their problems to make them comfortable like cook, maid good tv, bed, mattress, sofa, elder proof restrooms. These are to avoid any mishaps may occur due to old age (trip fall/ back pain/ knee pain etc)
I lost one of my parent when I was away it still bothers me. what if I was near to them. I could have did something which would have added few more years..