Setting vs. Culture
Question: I want to use setting of Victorian era London in my novel, but I don't like the culture, especially when it comes to the way they address each other.
What must I do?
Assuming you are writing some kind of fantasy (including science fiction or steampunk), the important thing is to be consistent. It's okay to create a story world that is set in an alternate history or parallel dimension that resembles Victorian London, but is different in several key ways.
You may have to find a way to justify things, since culture is often related to technology, development etc. A reader might wonder why the city still looks like Victorian London even though the class system (which determines things like manners, architecture, etc.) is different. For instance, maybe you postulate a revolution that brought about an era of social equality such that people stopped addressing others by titles or started using new titles like "Brother" or "Comrade" instead of "My Lord."
Of course, if you are writing historical fiction, that's a different matter and you have to know your audience. Readers of historical fiction fall into different categories. Some will love the period you are writing about and want that world portrayed as authentically as possible. They read historical novels as a way of learning about history. You have to do a lot of research to write this type of book, so you can get all the details, including how people interact, as correct as possible.
On the other hand, some people enjoy stories about characters with fairly modern sensibilities who happen to inhabit a historical setting. These books may present characters with very contemporary attitudes towards things like the status of women, racism, religion, etc. who nonetheless inhabit a pseudo-Victorian setting. These books are more like fantasies than true historical fiction.
Again, the important thing is to make your story world consistent. The reader should know whether the story is supposed to be a fantasy or an accurate reflection of history.