Shri newnewgen,
To the best of my knowledge, preta santhi is done when the normal after-death rituals are not done in the case of a diseased person. This is more important in the case of young persons and those who die due to unnatural causes or if the dead body is unavailable (like in plane crashes over the sea).
I don't know whether Mangalore is specialized in this line. I think any good vadhyar or purohit should be able to give you proper guidance.