Most of our Sins slice of life series is about the cast trying to make a family. The kids are slowly warming up to Human as they see that she cares about their mom, and them, she has money, and there’s potential to sucker her for treats. The twins are more reluctantly learning human ways and going to school among pitiful human children.
As the story progresses, the kids live with the human full time and call her "mom's girlfriend" and such. Human is an extremely doting mom and loves them. A lot of time, it’s just the twins and Human together while Demon is at work during the day with frequent trips back to the demon realm.
The Kids openly teleport to school. They don't hide that they are demons (so no sitcom-y junk about trying to blend in) but they have agreed to limit using powers in school. They are vastly too smart for grade school but they're mainly there to learn human ways, so they tend to slack off but can be amazing when they apply themselves. Usually when rewards are being offered. The twins very much follow the Sins tradition of being loot motivated, demanding of praise and majestic awe, and being total slackers easily distracted any time the world isn’t catering to their interests.
The Twins are also very much written as kids. They do stupid kids stuff and like kids games.
Like an exchange from off-screen of "Mom, the dog burped in my mouth!" "... why was your mouth that close to the dog's face..." "we wanted her to smell our breath so she knew what we had for breakfast"! Demon Mom is ashamed in the other room. We hear SFX from off-screen of the two kids now burping at each other. Human desperately trying to hold back laughter as Demon is deeply horrified at her spawn.
The Kids do everything together. We have an early story where their gym teacher puts them on opposite teams and they immediately go nuclear competitive with each other during dodgeball. They place protective wards on the ball so it won't maim their classmates but they're blasting the ball around, causing explosions, causing craters in the gym, shooting out blasts of demonic energy whenever the ball collides with something or someone, and creating shockwaves any time the ball is caught. As the school gathers to watch the gym class armageddon, the game never comes to a conclusion with just the twins left on the field, but the girls are pulled away for snack time and all is forgotten. The teachers collectively agree to never split them up afterwards.
We have a story where the girls get in trouble for fighting at school. Mom is in the demon realm, so Human is called and she rushes over thinking the girls are hurt. We find out the girls are blamed for starting a fight but they say the kid was a bully and they stepped in to help the kid being bullied. Human immediately turns it around on the principal blaming her for not supporting the teacher, leading to a known bully not being helped and endangering other kids to the point that the children in class are the responsible ones that feel the need to step up and help. Teacher and principal are flabbergasted and caught off guard and let the cast leave. The teacher winds up being grateful she didn't get blamed and that the human framed it as a failing of the principal.
The kids are shocked at what happened. Human is weak but willingly jumped into the kids' fight (they are so SO much stronger than her, rubbing it in), defused two antagonists and turned the teacher into a potential ally, all with just words. The twins respect diplomacy after this and warm up to Human, leading to them eventually calling her "Mom" too.
Mixed somewhere in there, we also get stories of how Demon Mom became a diplomat and how the couple met. We find out that human was a male client of the demon back when she was a succubus and went to her to get purposefully transformed. From this, the demon was intrigued that a human would seek her out for such a purpose and all the risks the journey had. We find this out because the kids inquire why Human has no pictures of herself as a kid. Human plays up her role as sitcom mom because that’s what makes her feel happy and like the person she wants to be.
It’s all a cute story for fun. No major changes to the Sins lore or big expansions on the state of the world after the end of Manitou. Just a look at what people in this world do when they don’t work for the Agency and aren’t involved in ancient evils popping up and causing chaos.