I've been thinking about the Celestial sibling's "age order" like who's the oldest and who's the youngest, specifically Solar and where he is placed.
If it was based on when they were manufactured: sun and moon are twins, but I don't think we have a time line bases between solar's original dimension and sun and moon's original dimension, like did it take longer for solar's original sun and moon to split? Due to how solar acted like when he was first introduced, I'd say solar's sun and moon split around the time eclipse made cosmos. And that means solar is a middle child
If we say that it based on maturity: terra would be the oldest, followed closely by solar and sun, then moon, and last but not least cosmos.
But what I think is the funniest option, that it's based on when they join the family: sun and moon, then cosmos and later on we got terra, and then Solar. Which to me is funny because imagine terra and cosmos get into another play fight over who is the "baby" of the family, and solar who just came home from a hard day at work and just to make them stop, he yells out 'if we base it on what point in time we joined the family, I am the youngest the sibling.' And before solar could react, his is suddenly getting jokingly babied by everyone