The Couples on Christmas after they've become their own little families (aka they got hitched) and actually have Christmas' alone together.

Percabeth:
Percabeth is the type of couple to wake up early on Christmas and wear Christmas pajamas to tackle a pile of presents under the tree. They're the type of couple to put on 'Rocking Around the Christmas Tree' and do weird dance moves in their kitchen until one of them doubles over in laughter and the other wraps their arms around them and they fall to the floor in giggles. Then they put on a slower song and slow dance for a while until Percy slips on a piece of wrapping paper and they fall over again. They keep the radio on but keep it on low volume so that they can sing along with each other, although sometimes it's more like screaming. They drink eggnog but Percy always dyes it blue; insisting it makes it better. They might drink something with more alcohol like wine but Percy hates wine and Annabeth doesn't really like it either so they either drink eggnog or hot chocolate or sometimes even champagne. But they both end up forgetting about their drinks anyway as they fall asleep on the couch during a cuddle.

Jiper:
Jason and Piper mostly just quietly open presents in their bedroom and sleep in and spend all day in bed. They're the type to send all their friends Christmas cards that won't get to their houses until after Christmas and put up their tree on Christmas Eve. They probably drink eggnog all day even though they both hate it and have a glass of wine or two before the day is over. They go to the rooftop and watch the stars before falling asleep and Jason insists every year that he heard Santa just before he fell asleep just because it makes Piper laugh.

Frazel:
Frank and Hazel wake up late on Christmas because they stayed up all night waiting for Santa. They bake Christmas cookies and Hazel flicks flour on Frank and he wipes batter on her nose. They take turns tossing chocolate chips at each other to catch in their mouths. They drink nonalcoholic eggnog and probably spend all day with the radio turned all the way up so they can listen to Christmas carols all over the house. They wear fuzzy socks and bathrobes and cuddle on the couch and lay on the floor by the Christmas tree and just talk. They watch the parade and marathon old Christmas romance movies and eat the leftover cookies from when they sent some to their friends.

Solangelo:
Nico and Will don't really celebrate Christmas much. Will puts up a tree and they exchange presents but they mostly just use the day to go out and ice skate and walk through New York. They play in the snow and Nico probably buries Will in snow then sculpts it so it looks like an angel or something. Nico wears a jacket, jeans, a beanie and maybe a scarf and he's fine but Will has to bundle up; a jacket and a coat, a hat and some earmuffs, two scarfs, two pairs of pants, three pairs of socks, snow boots, and gloves AND mittens before he stops shaking like a chihuahua. Nico makes him hot chocolate when they get home and they watch Die Hard in their pajamas.