Sylvan would have two social media accs honestly. One would be her main acc where she would post fit checks and stuff, that acc will be called @SyllyGoose. This is actually a reference to one of my Sylvan art where her milk carton box had the name "Silly Goose" on it (if you dk what I'm talking abt 👇) 
And one would be an acc for her boutique bc I would like to think she owns one in the future. It would be called @OutfitAlchemist or smth (I'm not good with names help 😭)
Hiro would also just use his full name so, @HiroTaye. He would probably think it's pointless to think of something creative just for a name 🥲🥲😓 it's also mainly bc he's just lazy 😭
Tanlin username would be @Error404TanTan. Bc she malfuctions every time she tries to chat with someone lol (unless she knows that person)