I’ve been on a sweet sappy domestic fluff stancest kick lately so here’s an idea (Note after the fact this is long and basically the outline to a fic)
Dipper and Mabel are Stan and Fords biological kids. I’ve seen some really fun AU’s where either Stans their dad or Fords their dad, or Ford and Stan had one each and coincidentally had them at the same time. For this idea I think it would be deeply funny if they slept with the same girl unknowingly and she calls them both up and tells them she has no idea which one of them is the father but doesn’t care she just wants them to take the twins.
Let’s just say she gave motherhood a shot but after 4 years she just couldn’t do it anymore. I think she does care for Dipper and Mabel but more in a wine aunt way than a mom way.
Stan and Ford meet her on neutral ground and meet her and the twins. They both instantly fall in love with the twins and agree to take them, with both of them raising them. Stan and Ford are identical twins in this so genetically speaking they’re both the father. (But they both individually think they’re the father and butt heads over it at first)
Things are still messy between Stan and Ford since they haven’t seen each other in 7 years and now have to raise kids together. (Ford has only just met Bill and hasn’t started on the portal) They keep it together for the twins and try not to fight in front of them. They reach a tentative agreement about what to do, with Stan moving in with Ford, and the two of them taking on the stereotypical breadwinner and homemaker roles. I wouldn’t say one is the mom and the other is the dad, I think they’re both dads. It’s the same thing for the husband and wife dynamic, they’re each others husband (for the kink it’s free game but we’re not there yet)
I think at this point their relationship would have been platonic in the sense that they hadn’t been sexually attracted to one another, but they both have some deeply repressed/misunderstood romantic feelings for each other (In the co-dependent emotional incest way)
They probably only make it two weeks without fighting and that’s only because they had been successfully avoiding each other. Dipper and Mabel have both picked up on the tension between their dads and they get it in their heads that it’s somehow their jobs to fix their relationship. Mabel likes to make them “get married” and have them tell each other “I love you” over and over again, while Dipper makes logical arguments on why they should be best friends forever. With both of them making using play as a way to force them to spend time together. Dipper and Mabel probably want a real family like the kind they see on TV, and they see their chance to have one once they move in with their dads.
One night after they put the kids to bed they both agree that they need to get their shit together because it’s effecting the kids. They get into a huge fight down in the basement that plays out the same as it did in ATOTS but with it ending right when Stan gets burned. They finally have a real conversation when they’re upstairs treating Stans burn. The fact that they have to whisper yell and that they’re not directly facing the other is the only reason they are able to get through it.
Ford lets Stan sleep in his bed while his burn heals and they both have feelings about it. Finally they stop avoiding each other and move on to trying to fix their relationship. Dipper and Mabel think that all their hard work finally paid off when that morning they wake up to pancakes and their dads laughing at something the other said.
Then it’s just moments of the twins being adorable as they bond with their new dads while Ford and Stan get closer.
• Ford staying up too late and forgetting he let Stan sleep in his bed, so he goes into his room and passes out next to Stan. Stan wakes up but doesn’t leave, he just grumbles something before going back to bed, and yes they wake up cuddling. Ford ends up doing it so often it becomes routine, even after Stans burn heals and they’ve had more than enough time to set up a separate bedroom for Stan, they don’t, and it becomes Stans room just as much as it is Fords.
• Mabel feeling left out because she’s the only girl in the house and the family taking her out to do “girl things” Stan lest Mabel pick out his apron and she picks the pink frilly one. They also play dress up which Ford unironically loves and Stan hops aboard the braid train and agrees to never cut his hair because she likes it long. (And yes, the apron absolutely does it for Ford)
• Stan and Ford absolutely have a kiss-it-better moment with the burn but after Ford can’t stop wanting to kiss the spot.
• Stan secretly buying a daddy issues book along with a number of parenting books that reads frequently because he can’t stand the thought of making his kids feel like he and Ford did growing up. Ford doesn’t realize until he finds his spare glasses missing and catches Stan up late taking notes as he reads wearing Fords spares. Stan has an eye doctor appointment ready the next day.
• Stan kinda gets obsessed with doing things to make Ford like/praise him. Most of which revolve around just taking care of Ford and the kids. But some stuff Stan can’t help but feel like it toes the line on flirting, but Ford likes it so he doesn’t stop. (Things like feeding him, using the same shampoo to smell like him, grabbing Ford by his waist, sharing clothes, ect)
• They take turns being the “mean” parent because they both hate it but also know that one of them has to lay down the law and put the kids in time out. Don’t make me get your father gets used a lot.
• Back when they were fighting they would compete on who could be the better dad and when they first made up they kept doing it but in a more playful way, until one of them has an insecure parenting moment where the other comforts them, and eventually they stopped thinking “these are my kids who I share with my brother” to “these are our kids”
• When people ask which one of them is the father they always reply “I am” which leads to much confusion to the towns folk. Stan and Ford make it worse when someone asks while they’re together and they both point to each other and in unison say “He is.”
• Dipper having a nightmare and waking up Mabel so that they can go sleep in their parent’s bed. With all 4 of them having a big cuddle pile.
• Stan and Ford unlearning toxic masculinity via the kids, with Mabel having them do “girly” things and them not wanting Dipper to internalize that he’s weak by any means.
• Ford loves playing with the kids, to the point where he finds child friendly adventures to take them on because he wants an excuse to work and spend time with them at the same time.
• They don’t tell their Ma that they’ve made up and that they have kids until literally months later. They just fucking forgot.
• At some point Dipper had disconnected the phone because it started ringing when everyone had fallen asleep after movie night. This leads to Fiddleford just showing up one day thinking Ford had finally gone off the deep end.
• Stan and Ford start doing the forehead taps nose nuzzle thing as a way to express their gay longing for each other without admitting that it’s romantic
• If they saw the rest of the Pines family for the holidays, Filbrick would be the one to inadvertently put the idea into their heads that they might be incestuous. Since up until this point they have both firmly been in the “this is a normal way to feel about your twin” stage and had never really entertained the thought that they might be anything else.  
• I can’t decide if I should go with my fave dynamic of Ford getting carried away x Stan going into tsundere mode or if it would be more accurate to have them kinda shyly test the waters between them. Or something else completely. Maybe they’re too busy being dads to really think about it and one night they kiss after a stressful day and from then on they’re just together.
• At some point Ford would accidentally refers to Stan as his husband before immediately back tracking—it starts a rumor among the towns people that they’re husbands pretending to be brothers because of the stigma against two men raising children together.
• They both cry on the twins first day of school, Ford cry’s first and Stan manages to hold it together until after they’ve dropped them off. And the twins start to experience separation anxiety towards the end of the day. When they get home they get caramel apple slices and cuddles. 
• If Bill was around during this AU I think it would be funny if Ford agreed to do the portal but hasn’t even started on it because on the kids (guy hasn’t even submitted the idea to the grant board) So Bill decides to talk to Stan and convince him to raise the kids full time (he tries to prey on the insecurities about how this is the only thing he’s good for) But Stan ends up cussing him out and basically just taking his frustrations out on Bill to the point where Bill actually fucks off for a while (he comes back when the twins are older to try again, but he’s fucking mortified over what Stan said to him)
• I really want a marriage scene between Stan and Ford, as unofficial as it might be, maybe it’s some mystical protection ritual where they have to promise their souls to each other to complete it, either way they get married and live happily ever after
That’s all I have for today but feel free to use any of these ideas, since it’s debatable on whether I’ll actually write a fic about it