Now! with the 4 seasons au, Feng Xin is already married to Mu Qing, Shi Qingxuan and He Xuan and they're all very comfortable step parents to CuoCuo (who may end up getting a different name with CuoCuo an inside joke type of nickname)

What no one is expecting when they leave lil CuoCuo with a barren Lan couple who were away from Cloud Recesses for a few years so they can easily hide a non existent pregnancy, is for the boy to not only cry out for his birth parents, but to also cry out for his step parents, aunts and uncles. Originally it was just going to Jian Lan and Feng Xin visiting but they keep seeing how much their son misses everyone so... they take turns/visit when they can.

They also let lil Jingyi know they're keeping an eye on him with small moments of divine intervention. He Xuan has him be splashed by water when he's by the docs, Hua Cheng leaves a silver butterfly for him to find, Qingxuan causes an extra strong breeze when he's somewhere windy, Mu Qing leaves little silver ornaments for him to find and easily hide, Jian Lan leaves books for him in his Qiankun bag etc

they all do small things to ensure Jingyi knows he's loved.

now, for the reveal. Having it take place post MDZS cannons makes the most sense. Maybe Jingyi is on a night hunt by a river and falls in, sure he's a good swimmer but even good swimmers struggle when they're panicking. Then, while the rest of the Juniors (and Wei Wuxian) are panicking, they see a figure rising from the waters. They look similar to a fierce corpse, pale and dead. Then they see who the 'fierce corpse' is holding and breath a sigh of relief that Jingyi is safe.

Then several more well dressed figures appear and fuss over an unconscious(?) Jingyi, with a well aged woman and tall scowling man leading the charge. Maybe someone notes their similarity's so Jingyi in terms of appearance

And so it spirals from there, maybe someone challenges the gods (and ghosts) to a fight trying to 'save' Jingyi who wakes up just enough to mumble "mama? baba?" when he sees Feng Xin and Jian Lan who are holding him and that causes a lot of confusion. Especially for Lan Sizhui who was literally raised alongside Jingyi and has met his Lan parents.

Just a whole spiralling mess that results in the whole family basically having a meeting with Lan Qiren, Lan Xichen, Wangxian and maybe some others where they have to explain 'So he's our son, no we're not married he's married to those three, the others? they're aunts and uncles, yes they're gods, yes I'm a ghost, no I'm not a young ghost I'm over 800 years old... wait CuoCuo is too...' just them being very casual about the weirdness and the MDZS crowd are just very confused and staring at these people and then looking to Jingyi who's just sat to the side watching everything while eating chicken with Qingxuan and Mu Qing fussing over him.

Yeah... life is weird and Jingyi has the wildest family tree. At least there's an explanation for his biting habits as a toddler

Quick note on parental terms:

Jingyi, in public, calls his adoptive Lan parents Mama and Baba, in private he calls them 'Lan mama' and 'Lan baba'

Feng Xin he calls baba and Jian Lan he calls mama

Mu Qing was jokingly refered to a 'a-die' once and it stuck so now he's a-die

Qingxuan is xiao-mama or xiao-baba depending

He Xuan has been stuck as A-Niang since Jingyi was 7 so that's sticking

Pei Ming is Da-Jiu and Ling Wen is yima

Hua Cheng is shushu and Xie Lian is bofu

that's not even accounting for all the 'gege's' and 'jiejie's' he has with the heavenly officials