sj
the parents chinoch of their children should be primary.
they may wish to instill a certain kind of respect for adults partly by the mechanism of titled names.
or perhaps their chinuch should be that the children should respect whatever preferences the adult prefers, in your case to be called by their first name.
the first is much easier for the child, more consistent, and my personal preference.
but in any case the primary determining factor should be what the parents have decided is best for their children
mrs shira is a nice compromise