First names, both sides of the family.
I have only one left, and I call her Aunt X. My cousins, surprisingly, just call her X.
Unrelated? Do you know what the words Aunt and Uncle mean??
Lots of people have “honorary” aunts and uncles. Often it’s a close friend of their parents or even an honorary aunt/uncle of the previous generation.
My sister-in-law is Aunty (Name) to her friends’ kid. Doesn’t seem unusual to me.
One of my aunts told me last year to call her by her first name, as calling her aunt made her feel old (she is only 83).
In my partner’s family, some of the nephews are older than the uncles, so just about everyone calls each other by their first name.
The only aunt I addressed by her first name was my mom’s sister, and that’s partly because she wasn’t much older than I but mostly because she was mentally handicapped, and from the very beginning, she was too much like a child to be an “Aunt.” Even my daughter and my sister’s kids used only her first name. But for all other circumstances, the appropriate title is affixed. It just seemed a proper sign of respect to an older generation.
I never referred to any cousin with “Cousin” and their name - it didn’t seem necessary.
As a kid, it was always “Aunt Firstname” and “Uncle Firstname”.
But later on…well…it got complicated, since one Uncle Firstname had Wife #1, Wife #2, and Wife #3.
Uncle Firstname is called just that. It hasn’t changed. My cousin also calls my dad “Uncle”…as they compare war stories. So she’s not dropping the honorific, either!
Aunt #1 (Uncle’s first wife): I call by her first name only. They divorced when I was quite young and I hadn’t seen her in decades. It was weird to call her Aunt Sally, and she asked me to use just “Sally” since I was 44 when we first ran into each other again.
Aunt #2 (Uncle’s second wife) – Basically the same thing, even though I’ve seen her pretty reguarly. She felt it was weird now that they’re divorced, she’s remarried, and I’m getting grey hair and wrinkles (though she didn’t put it that way).
Aunt #3 (Uncle’s third wife) – He married her when I was an adult, so I have always called her by her first name.
I’d also called my mother’s cousin and her husband “Aunt” and “Uncle” while growing up. They also asked me to switch to their first name only once I grew up.
FWIW, I’m 45. My mom’s family are from New York/New Jersey. My dad’s are from West Virginia. We all lived in Florida from about 1978 onwards.
And if you think that shit is weird, you should’ve been at Christmas breakfast this year. Me. My cousin and her husband; their kid. My idiot brother and his second wife. My nephew. My dad and his second wife. My mom. My uncle and his current wife. And his first wife. And his second wife and her new husband.
I figured he meant related but only by marriage…
It’s not unusual - but people generally refer to those as “honorary” not “unrelated”, just like aunts and uncles “by marriage” or “in law” are generally referred to that way rather than “unrelated” when for some reason it is necessary to distinguish them from blood relatives. I didn’t know if the OP was talking about an unrelated aunt being a female friend of his parents or his mother’s brother’s wife.
I always called my aunts and uncles by “aunt” and “uncle” - but only aunts and uncles. Not my parent’s friends and not my mother’s older cousins. Every now and then, one of my uncles would refer to me as his children’s “aunt” and I couldn’t stand it ( although I could kind of understand it, because age wise , they were pretty much dead in the middle of me and their kids. One uncle is 16 years older than me and the youngest cousin is 18 years younger than me)
When personally speaking to my uncles and aunts I have always called them by their given name. When addressing them in a letter or speaking about them with my parents, sisters or other relatives I would use “Uncle GivenName” or “Auntie GivenName”.
Good heavens no! You’ll be missing out on being called Great Aunt (or Uncle) Kunilou! 
I have an aunt whom I saw frequently as a child and who even lived with my family at one point – she has always been [first name] to me, and when she got married, her husband became [first name], too. They live a few blocks from me in the same town.
My other aunts and uncles live on the other side of the country, and I see them once a year at most, usually once every 4-5 years – them I have always called Uncle or Aunt [first name].
Aunt Firstname and Uncle Firstname. Same for the non-related aunts and uncles (actually, I think there was only one non-related couple I called aunt and uncle).
One of my brothers makes his kids append “aunt” in front of my name. I don’t like it. The rest of my nieces and nephews just call me by my first name.
I too was raised that you never called aunts or uncles by their first name alone, always Aunt X or Uncle Y. I suppose now that I’m older I could call them by their first names, but that would feel uncomfortable.
With the aunt and uncle I’m closest to, I just call them Auntie and Unk. For the rest it’s still Aunt X and Uncle Y.
Interestingly (probably not), I was born and raised in the North, while my cousin who was born and raised in the South just uses first names. Just a matter of personal preference I guess.
Since I had three uncles and three aunts and all of them were named Harold (uncles) and Betty (aunts), for matters of expediency, I always referred to them as Aunt Betty Lastname or Uncle Harold Lastname.
It would be as weird as calling my parents or grandparents by their first name. You don’t get to do that just because you get older, either.
In fact, unless someone has stated another preference, I pretty much call them by the name I called them when we first met. You can pick up an affectionate nickname, but I’m not going to start calling you a different version of your real name.
I’ve always addressed my aunts and uncles by just their first name.
Just like I do with my parents.
My parents were kind of weird for ex-military in the 60’s. We were never required to say “sir or ma’am”. “Yeah” was perfectly acceptable instead of “yes”. I once had a teacher who went ballistic when she asked me something and I answered “yeah.” “How dare you! When your mother asks you a question, do you say “yeah” or do you say “Yes, ma’am”? “I say ‘yeah’.”
I was genuinely puzzled while she thought I was being a smart ass. That was a fun year, let me tell you.
My parents grew up in the same town. My mom’s siblings were Firstname always. My dad’s siblings were Aunt Firstname and Uncle Nickname. Somewhere around high school, I thought that calling men and women in their 40’s and 50’s Sonny and Sissy was ridiculous. I refer to all my aunts and uncles by their first names. I don’t usually CALL them anything. I find that saves a lot of trouble all around.
I used Aunt and Uncle for mine. One of my wife’s aunts lived with them, and that was a first name basis, at least when I first got involved.
My kids have only one uncle, and he goes by his first name, especially now that they are grown. But I don’t think he’d like to be called Uncle.
I don’t use titles.