I see what you mean re: Spike being the center of Happy Family OT4 fics. Even my favorite fic 'verse (you may need an account to access it) there's more Spike/Buffy, Spike+Tara and Spike+Dawn. There's implied, periphery B+T and D+T, but I've come to realize over reading this 'verse a thousand times or so, as a whole it really is Spike's story, from Spike's point of view, even though parts are written from Buffy's perspective. I think it's the same way season 1 of The Vampire Diaries (don't remember if you watch or not - it's fun, but not as good as Buffy), where we're introduced to the series through Stefan's perspective, even though it's Elena's story.

But yes. Happy Family OT3 in theory, if not in practice.

Also, I don't really like Spike/Tara either. I think it negates how progressively the series portrayed Tara's sexuality - making her fall for a man after declaring herself a lesbian. I know sexuality is fluid, and on a spectrum, but because of the marginalization of LGBT characters, I want to keep Tara gay because LOOK! IT'S ACTUALLY A POSITIVE, NON-CLICHE GAY CHARACTER! I don't know if this is an unpopular opinion that will get me in trouble or not, but I just want to keep Tara gay so that we have that 100% lesbian figure in the 'verse (Willow is a lesbian as well, because that's how she identifies herself, but I think her sexuality is more flexible than Tara's? Does that make sense?).