Okay but the dynamic between the Twins would be so interesting though
Annabeth would be all "the fuck you looking at?!" when it comes to gods and their wondering awooga eyes because, and bless her, Percy is so oblivious when it comes to romantic interests like half the camp was falling head over heals to impress her and the other half had a bi/lesbian awakening and Percy didn't notice but when it comes to Athena? Poseidon? Percy would be the main speaker, the shield for Annabeth, the rip rap to protect the cove. For Percy, Annabeth is the scary dog privilege around all the gods but their parents.
Percy, would be her usual self but with her loyalty and protectiveness all focused on Annabeth. Oh some god is trying to flirt with Annabeth? yeah, she's going to stab him. No worries. But if they're around Athena and Poseidon?
Annabeth has had no positive parental figures outside of Sally Jackson and Chiron (Paul gets an honorary mention) and has no idea how to navigate the parental minefield that she is in. Percy knows how to navigate messy family drama (thanks smelly gabe) and so will always throw herself in front of Annabeth to shield her from anything remotely similar to gabe or the Chase's
Poseidon canonically loves his kids. He ruined Odysseus' life over one of his sons injury. If you give him the Twins, if you tell him Arsinoe and Perse are his, and that they are terrified of him, that they are expecting him to treat them like Zeus treats his children? And that his daughters prepared and decided who among them was to protect the other? His heart will shatter.
Poseidon would gift Arsinoe literally everything until he finds out she likes architecture and then he will make her the official architect and literally do anything to make her smile as brightly as she did when she saw Atlantis for the first time.
Amphitrite would be soooo happy to have double the seal pups to spoil.
Triton would be upset at the Pallas look alike but then he sees his younger sisters spar and he's determined to not let either of them fall to a spear.
Kym, Rhodes, and Ben already outnumbered their father and Triton, but now they have two more sisters?
Athena would have no idea what to do. She faintly remembers her mother, other mothers that she could look up too have either really bad relationships with their daughters, or they were kidnapped from them, or just don't seem like the type of relationship Athena wants to have with her girls. She wants to know why Perse is so protective over Arsinoe around her. She wants to know why Arsinoe looks at Poseidon like she's about to cry from happiness every time he asks her if she want's to design a temple
all in all, lots of angst potential