Brother & Sisters, Aunts and Uncles.....husband and wife
In the rural Southern US, children were not to call adults by their first name, JW religion or not. Anyone not well known as always Mister so-and-so, or Miss/Mrs so-and-so. Adults close to the family would be called Uncle or Aunt, even if not really related. Like your father's best friend would be Uncle Bob.
In the JW religion, all adults were called Brother or Sister (followed by last name) by children at all times. There were some people I never knew their first names growing up.
As for adults, the use of Brother/Sister was usually confined to JW settings - Kingdom Halls, field service, assemblies, and usually with 'friends' that were not in your close circle of friends. But it was used enough even in some situations that sometimes it made adult JWs stick out in public when they referred to another adult as Brother or Sister.
Never called any of the brothers and sisters in the KH aunt or uncle, none of the kids did. My parents had many friends when I was growing that they knew before my mother got baptized and instead of calling grown folks by their first name it was always Aunt or Uncle, but not the folks at the Hall.
It used to drive me freaking nuts before or after a meeting when a " brother " or a " sister " would come up to me and ask, " Hello Brother Flipper ( by my last name ) how are you doing today ? " I'd just say to them, " Oh, hi John " or " hi Nancy " then sometimes when I'd get really annoyed within myself I'd tell them, " Please call me by my first name, O.K. ? It feels more comfortable. " So I'd just speak up.
All mind control cults do this to replace our real families so that it programs the cult members mind to be more attached emotionally to the fake " brothers " & " sisters " with the same indoctrinated beliefs. It's ridiculous. Just your garden variety brain washing and mind control which many religions and mind control cults use to control people and WHO people in their organizations consider as " family " . It's actually creepy as hell. Creeps the you know what out of me. One reason again that child abuse is rampant in organizations like the JW's. Too much trust without any check systems. Uncle " Jed " or Uncle " Bob " sitting in the middle of the kingdom hall befriending young kids might be Uncle " Pervert " or Uncle " Twisted " - and none of the J-dubs even know due to TOO MUCH blind trust in each other. Scary scene man. So WT Society leaders get what they deserve in child abuse lawsuits due to no check systems. Peace out, Mr. Flipper