Hmmm Gomez and Morticia adopting Percy because of Hades killing Sally when he was 10 to get at Poseidon and they found him nomading around the US since there's no way he was staying with Smelly Gabe and refusing to let anyone else be his new parents due to his crazy ass powers,how he'd been using them to do vigilanteism unintentionally by doing stuff like saving people getting assaulted and his personality making him perfect to be an Addams,including the willingness to kill,so he becomes the eldest Addams sibling and a goth punk instead of crustpunk like in canon.They also nickname him 'Seo'(spanish pronounciation)instead of Percy from his full name 'Perseo' and years later Sally gets brought back from the dead through macabe shenanigans and is the family's live-in ghost