I Am Probably The Last Person To Realise This:

I am probably the last person to realise this:

Artemis is the older sister of Apollo. Her colours are silver and she has black hair while Apollo's colour is gold and he's blonde.

Thalia is the older sister of Jason. Her weapons/jewellery is silver and she has black hair, while his weapon is gold and he has blonde hair.

Artemis prefers the appearance of a young girl and Thalia while physically be always 15 (a "young girl").

Apollo and Jason are both the disfavoured child from their father.