Yeah, the history is interesting.
I'm having problems finding anything about the origins in the library, so thank you to Faeril for the context that it started at least as early as 2004, although I'm guessing earlier? If someone could give even more context that would be great.
The "First Sister Ceremony" was first recorded in the library in October 2006.
The implications from late 2006 have First-Siblings being a very serious commitment where you have to petition the Amyrlin Seat, go through pre-bond counseling with a Gray, and the live ceremony is mandatory. At the time the linked article was written, there were only six pairs of first siblings. However, the 2006 Admin Meeting notes say that "we will limit the amount of first sibling ceremonies we preform at real life events (people are still welcome to perform these on their own if they want) due to time restrictions. Unless otherwise stated, we will honor the first three requests we get for any specific event," which suggests that it was a quickly growing pool.
As of the 2010 Admin Meeting, they were no longer officially recognized and the Tower no longer presides over or puts limits on first sibling recognition.
The image of you sending your sibling flying across the room is forever imprinted in my memory. That was before I had a cell phone tho, so no videos from me.