This is probably the best headcanon I've ever done:
Sometimes I made stories about what is going to happen with the seven (and Nico too) after they die. I imagine a final battle (with Uranus for example) and the phophecy that says they will go together and punch Uranus in his heart with their swords at the same . Because Uranus is very strong ,they will die while stabbing him. Close to death, they will be holding hands and Percy and Jason will say: I'm not scared to die if you are with me. We will die as a family, and be together forever as a family. We will go together in Elysium.
Then,they die and their shadows appear.
Thanatos appears too,ready to take them to Underworld.
After that,the gods will appear, when Uranus is finally gone, and take their children to Olymp. There ,they will decide to make them immortal.
They will spend the summer at CHB teaching other demigods with Chiron and when the summer is over they will be like 'The guardians of good' (I couldn't think of a better name lol) and they will travel around the world together and make good things ,like helping people,saving the world, etc (and also they will spend time with their immortal parent sometimes,when they aren't in an adventure)