(Pertaining to my bonespreg)
Making Joanna McCoy a funny strange girl is so important to me. She's an amalgamation of everything I love about my sisters and cousins. She's bad at math and science and SO into theater, music, language, and she's slowly becoming a history buff by accident. She has her dad's temper and compassion, and her mom's ability to persuade and influence a room. She's very funny, in a deadpan-sarcastic sort of way. Loves to fuck with people by saying completely made up "facts" with a straight face. She collects junk and vintage technology, and she experiments with her self expression a lot.
The second important part here is that her parents support her SO much. And not just McCoy and Jocelyn, but also Jocelyn's husband, Beau. He takes his role as bonus-dad seriously, and he's been her stepdad since she was like 6. He's her "Let's go get iced coffee" parent when she's pissed at the world and her mom's not fair and her dad's in space and school sucks and life sucks and everything sucks.
She's got a lot of pressure from her teachers to apply herself more in STEM because, obviously, McCoy is a trailblazing surgeon and Jocelyn is a renowned astrophysicist, but at every parent-teacher conference, again, they're like, we're not going to tell our daughter she has to go into a STEM field if she feels like preforming arts is the right move for her, and they're 100% behind her ambitions.
And she's a pretty honest and good kid, too. She gets in a little trouble, but she's really that one kid that straight up tells her parents when she's planning on sneaking out or doing something stupid. They communicate pretty well and while she has her own secrets, like all teenagers, she knows she can talk to at least one of her parents about whatever issue she's having.
This is all important because Spock's being introduced to this established family dynamic, this really functional family, and he doesn't know what to do. Him and McCoy are having a kid together, which inherently disrupts their unit, but also, at the time he gets pregnant, they aren't involved whatsoever. He's never met any of McCoy's family. He knows of them, but doesn't know anything about them.
As he gets more involved, though, he's realizing he doesn't really want his role with Joanna to just be "my sibling's dad," or even just "my dad's friend/boyfriend." He had worries from the start about creating an imbalance between the children and wondering how he was going to make sure not to exclude Joanna in whatever the future held, but it takes him a while to realize fully that he actually wants to be integrated into the *existing* family unit, and he does not know how to express that at all, even after him and McCoy get together.
Meanwhile, McCoy is like, Spock never asked to take on my whole family, I've never introduced a partner to my daughter. Could you even consider themselves "partners" when they're just coparents in a situation? And already making Spock a dad when he hadn't planned on it seems bad enough without placing expectations on him to step into the role of stepparent. Plus, his daughter is almost grown. So McCoy has no expectations of Spock, and Spock isn't pushing the issue even though he'd really like to.
But there's going to be circumstances that bring Joanna onto the ship, and that's where they start to find a groove. It starts with her asking a bunch of nonsense questions just to mess with him, but ultimately it'll turn genuine, finding that she likes the way he explains stuff and is willing to have long winded discussions, and this leads to her seeking him out for unbiased insight on some of her issues.
He figures out quickly how to tell when she's having him on or not, and they develop their own sort of deadpan routine from it where he'll respond to her "facts" as if he doesn't know they're made up. On top of that, when he catches her doing it to someone else, he just agrees with her. McCoy says it's illogical to spread false information and Spock says it's a good lesson to always be certain to check that your source is correct. (Aka; yes i know it is) Don't worry, though; he will not be spared from the wrath of a teenage girl.
Like I said this fic is self indulgent as hell, I'm having all too much fun plotting this course for these guys. What an exciting time for them all