Oh. I had no idea. When was his family mentioned? The comics? If so, that's probably why I wasn't aware. I've only ever read a few comics that took place in between STV and STVI..
Mind Meld doesn't fit with the modern novelverse anyway, portraying Rigel V and the Rigelians in an incompatible way.
I asked John Vornholt about that a few years ago when I wrote an article for Star Trek Magazine on Sybok. The back cover identifies Teska as Spock's niece (so, Sybok's daughter), but the book was very vague on that point. The intention was that Teska was Sybok's niece, but Paramount Licensing didn't want to touch Star Trek V and its Apocrypha button, so her parentages was deliberately left vague. One interesting thing about Sybok that I noticed when writing about him for the magazine was that his Treklit appearances all take place in alternate histories. He's in Geoff Trowbridge's Myriad Universes novel (I think it's Geoff's, now I'm not so sure), and he appeared in DC Comics' "Convergence" in an alt-24th-century.
As I recall, I wrote the back cover copy for Mind Meld, but back in those days all I ever saw were the original outlines and proposals, not the final manuscripts . . . . But I don't think ST V is all that apocryphal. Lords knows I've referenced it in my novels before--and even gave "God" a supporting role in my Q trilogy.
Roddenberry considered much of ST V apocryphal, but it's been decades since his narrow definitions of canon have been honored by the studio or licensees.
Sybok appears in mine and Michael's Myriad Universes: The Tears of Eridanus, as one of T'Pau's war-leaders. He goes around telling people to embrace their pain before he hits them. Sulu beats him up.
"Decades," Christopher? Not quite that long. Besides Vornholt, Susan Shwartz said something similar when I asked her about Sybok's non-presence in Vulcan's Forge.
But why? Just because it was mentioned the first time in a film, and not in the holy 60s TV show? Kirk got a son in the town of Fucking, NW. So why can't Spock have a half brother from the same place?
Look, for better and for worse, ST V is just as "canon" as all the other Trek movies. Heck, the recent Enterprise "Owner's Workshop Manual," published just a few years ago, references it with regards to the layout and modifications of the Enterprise-A. If people tend to stay away from Sybok, it's not because there's any question of the movie's place in the continuity; it's just because ST V's reputation is such that nobody is a big hurry to dwell on it. "Yeah, it happened. Doesn't mean we have to mention it if we don't have to." It's the same reason you don't see a lot of sequels to "Spock's Brain" or "Turnabout Intruder." It's not that they've been "officially" deemed apocryphal; it's just that they're unpopular enough that authors and editors tend to steer clear of them--for good reason. "Hey, I've got a great idea. How about an epic trilogy focusing on Sybok of all people? You know, the guy from that movie nobody likes?" "You're joking, right? What else have you got?"
I actually think Sybok was the best part of the movie. There's a ton about it that doesn't work, but Sybok is not part of the problem. Okay, there are some unexplained bits like how his power works, but Laurence Luckinbill made him an engaging character.