Blue Horizon has 14 sets of twins and triplets. Here's a list of several who will appear in Book 1~!
(Originally on Tumblr on 03/23/2023.)
Here's a post with Blue Horizon's book 1 twins + triplets~ ᕕ( ᐛ )ᕗ
🌊 🌙 Antonio, Fernando and Raj Chandrani-Rivera
🌑🌌 Armando and Antonio Herrera-Rivera
☀️☀️ Alejandro [Caldera]-Altaha's binary star
🌀🌀 Yasir and Karim
🪬🪬 Erika and Irina Musa
☀️☀️ Liliana and Lana Caldera
🌑🌑 Antonio Chandrani's cousins Mario + Maria
💧💧 Hazan and Hazal
And about 9 or so characters who are either spoilery or aren't intensively noted in Book 1. 1 is part of triplet OCs I didn't note.
Overall, the amount of Blue Horizon twins and triplets aren't only for the themes/metaphors/cyclical story--when I was 14 to 16 I just decided that in their world they just have more twins than on Earth and thus slowly kept adding twin characters.
Update 07/07/24: I remembered a final pair of twins that made it a likely-total of 15 pairs and trios (unsure but I tried counting) pretty late, but Alejandro has an older brother and sister named Mateo and Julia who are twins. They're the only ones who particularly escape twin-theme naming aside from Yasir and Karim I think and technically Tono, Nando and Raj (hard to not rhyme certain Spanish names), so might as well note them here.