Huh. My father and his sister always referred to each other as Brother and Sister. Not in the South, though, they were both Californians.
I have 4 brothers and a sister (I’m a dude). I don’t think I’ve heard anyone call her by her given name unless it was to someone outside the family. Most of us call her Sis or Sissy, or Twist.
I’ve never heard anyone call their siblings Brother/Sister/Sissy etc. Not sure anyone does here in the northeast.
Closest I can offer you is a friend’s youngest calls her oldest Brobo, but the little guy is only 15 months old.
Never heard anything like it, except for my sister whom we called “Suzie” (from Dutch zusje, "little sister).
I’ve heard it done with “sissy,” but it’s completely alien to my family.
We call my brother-in-law’s wife Sister-woman, and her children are no-neck monsters.
Tennessee makes us do it. But I think I would anyway.
Maggie
I’m in the UK and I call my only brother “Bro’” some of the time. I think it started with my school friends calling him Springtime’s bro’. I also call him Superbro now and then 
I know a family with two sisters and two brothers, and they call the older brother “Brother.” Sometimes they get very East End and call him “Bruv.” They’re all around 70 now. New Englanders since the 1600s.
I have never heard of anyone being called brother within their family. I have one old long dead relative that was known as Sis.
I’ve never heard of this.
Eh. Childhood nicknames can stick through adulthood. Especially ones used in the family. Buzz Aldrin picked up that nickname because his then baby sister couldn’t pronounce “brother”, it came out “buzzer” and “Buzz” stuck. Pretty useful nickname for an astronaut, if you ask me.
^ I would prefer it to “Deke.”
We called my one sister “Sis” or “Sissy” until she asked us to stop when she hit Jr. high school. I think it’s a southern thing; mom’s from Alabama.
I have three younger sisters and one younger brother. We always called him by his given name. One of my sisters, who has a daughter, married a man who has a son, and they had another son together. My older nephew calls my niece by her given name, while the little one, now 4 years old, has always called her"Sister," so that’s how we aunts refer to her when talking to him, ex: “Go get Sister, tell her dinner’s ready.” Not sure where he got it, maybe from the Berenstain Bears.
i havnt heard of iteither,and im have three sisters and am the only boy in my family
My grandfather had 3 daughters and one son. Evidently it was hard to pick a name for him since grandpa referred to him as “The Boy” as long as they lived.
I’m not sure I can accurately remember all the Brothers and Sosters in my family. 7 grandchildren, onky one male. His sister was called Sister by all of us. She’s 46 and my aunt only uses her real name when she’s mad with her.
My children were the first great grandchildren, so I thought my son would be his generations Brother. Nope. They all use proper names.
On Mother’s side of the family, there are Brothers and Sisters going back generations. I could never keep them straight. I only remember that it’s an honorific of sorts. My dad is called Brother, even though he has an older, still living, brother! I think that’s because older brother is not financially or emotionally supportive to the family, so his ‘title’ fell to my father.
People are very clannish in Mississippi, especially those that grew up country and poor. My grandparents (all dead in the last 10 years) and their siblings all experienced significant losses to war and diseases, and I think poverty, too.
To have a Brother or Sister had responsibilities, and not all of a given generation had direct male siblings. My generation just had the one. Brother.
Aah I feel like I’m on a rambling phone call with Mother on how things have changed, all for the worse (they’re not worse! They’re not!)
My group of cousins acted like siblings, but our children don’t care one bit about each other.