"our servants who used to be bahun and chettris used to call me Sirista Babu. They didn't even know how to say Shrestha correctly"
your sentence is a perfect untrue  1. every1 can see it.
Let's assume it is true, but
Servent yedi bhaye pani kina servent ko surname(cast) mention gareko. U can write the name of the servent,  like falano dai or didi or kaka or kaki. your are pointing their surname(cast).
U know the truth well. It's upto u.