I wonder if in time all of these titles will fade into obscurity? If you think back a hundred years or so it was fairly 'normal' for the term 'cousin' to be used as a form of address, e.g. "Good morning Cousin Elizabeth, you are looking well". Brother and Sister were also once used as forms of address, perhaps not followed by the given name, but as a stand alone. These uses have long since disappeared.
More recently I have noticed increasingly that families are dropping the terms 'Aunt' and 'Uncle' as forms of address. In my immediate family the GC tend to use just the first names when talking to their aunts and uncles; when my children were little they dropped these titles in their mid-teens. My DH and I, on the other hand, used the formal address Aunt(y) and Uncle well into adulthood.