There's a scholarly book called "Latin forms of address" that was published
in the last couple of years by a professor at Columbia that will give you as
good an answer as you are likely ever to get on how Romans addressed each other
both formally and informally in Latin.
I would like to recommend a book by the late Keith Hopkins called "A World
Full of Gods." It's an adventure in Pompeii before the eruption. The narrators
are two twentieth century students who have been transported through time and
are reporting on daily life in Flavian Pompeii. It's very good, because Keith
Hopkins was a great scholar and teacher.
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