I have been thinking about this and I have decided that I was completely wrong: this entire mess is Poeâs fault, he totally started it.
accidentally! and with the best of intentions! he woke up in the desert with the ship and Finn both missing, and while he feared the worst, he still had hope. when he made contact with the Resistance, he tells them about Finn and has him listed as MIA; he felt responsible for the kid, he felt awful that this boy took a courageous leap with a total stranger & got smashed to bits in the desert for his trouble.
Poe has some vague notion that if Finn was ever found, heâd ask him to join the Resistance, or help him get settled in a new quiet life somewhere safe. He knows Finn doesnât have anyone else, so he writes âFinn Dameronâ and lists himself as next of kin.
when they reconnect, heâs so happy that Finn is okay (a bit distracted by how gorgeous the kid is, he hadnât had time to notice before), and genuinely touched that Finn kept his jacket, that Finn was equally worried and upset over him. it occurs to him that the name thing could be awkward, so he explains his concerns, he explains next-of-kin notifications, and âyou didnât have anyone else that I knew of, so I wanted to make sure youâd at least have me.â
after that, Poe doesnât think anything of it.
âŠbut Finn! Finn is like, COMPLETELY VERKLEMPT, that this cool dashing hero person was looking out for him!  Finn has people now - he has Rey and Poe, and the entire rest of the Resistance have embraced him wholeheartedly. also!!! next-of-kin, thatâs SO NICE, he has kin now, heâs not just cannon fodder whose passing wonât matter to anyone but his squadmates. heâs a person, he has kin, he has people, he belongs. itâs so great.
he tells Rey all about it and she gets why heâs excited; it IS awesome. he signs everything âFinn Dameronâ and she addresses her messages to âFinn Dameron,â itâs all very exciting. and she thinks about it, too, she thinks about next-of-kin, about Finn coming back for her, Finn choosing her.
when she rejoins the Resistance, she asks Finn if she can be âRey Dameronâ so that they can have next-of-kin too. (it simply doesnât occur to either of them that they can get next-of-kin notifications without exchanging surnames; Poe did it that way, and it made sense to them, and they never thought about it beyond that.) and of course Finn agrees!
he forgets to tell Poe for another five weeks, and then mentions it in passing. Poe is like, professionally unfazed, so he just finds the whole thing charming. they are so cute and he canât stop smiling over them; they are the best. and again, Poe moves on & doesnât think anything of it.
âŠ..and then. AND THEN, eventually, Rey finds out that sheâs a Skywalker. [This was foreshadowed so heavily in the movie, Iâm 99.999% certain theyâre gonna go there.] and obviously thereâs a lot of feelings and drama, but when it dies down a bit, sheâs hanging out with Finn and theyâre drowsily curled up together on his bunk because they want to talk FOREVER but theyâre so tired but the have SO MUCH TO SAY.
Rey doesnât totally understand what all of this means for her, what it means to have that family and their legacy. but she does know what it means to have THIS family, the one she has with Finn. so it makes perfect sense to make him part of her new family, to mesh the identity sheâs inherited with the identity sheâs made, so she asks him, âyou are my people, you are my next-of-kin. do you want to be a Skywalker too?â and of course heâs like âYEAH!â
and like. throughout all of this, Poe is their buddy and means a lot to them, and they think of him as their people. (the entire Resistance has noticed how much the kids adore him & hero worship him, itâs hard to miss; they would tease Poe more about it, but he clings grimly to his virtue and hisses âCRADLE ROBBINGâ every time it comes up, so they mostly let it go.)
so when thereâs some Big Dramatic Space Mission, and his squadron goes missing briefly, Finn & Rey are both really messed up about it. and then one of them is like, ââŠyou know what we forgot to do?â and the other one is like âOH OF COURSE.â as his next-of-kin, they have the right to get his records updated, so thatâs what happens while Poe spends several miserable weeks fleeing across the muddiest, swampiest continent in the galaxy. when he finally makes contact with the Resistance, he has acquired (1) space cholera, (2) space ticks, and (3) a new surname, though he doesnât learn about that last one for a while.
His mothers find out around the same time he does, and they are Not Amused. âWhy wouldnât you TELL US,â they ask, and âitâs hardly classified, apparently your whole base knows,â and âwe had to hear about it from your commanding officer, young man,â and âwere you ever planning to introduce us, what do you have to say for yourselfâ
and like, thereâs a totally reasonable and rational explanation for all of this - âitâs not what you think,â he says feebly, and his moms huff, unimpressed - but heâs still shaken up from the influx of engagement/wedding presents and General Princess Leia herself visiting his bedside to fix him with a gimlet stare and a completely deadpan, âWelcome to the family.â Heâs had a long day, he might be married, and heâs not sure how but itâs at least 30% his own fault.