Yes, you read that long title correctly. Here I’ve taken the time to explain in the simplest way possible (which, as it turns out, isn’t that simple) all of the characters from 12th Night and how they are all related. YOU’RE WELCOME.
Viola loves Orsino who is her boss, who loves Olivia who loves Cesario who is really Viola in drag.
Sebastian is Viola’s twin brother who marries Olivia which causes Orsino to fall for Viola (while, I might add, is under disguise as Cesario.)
Malvolio is the only serious one in the play who is tricked by Maria who is Olivia’s gentlewoman. Malvolio loves Olivia who loves Cesario who Malvolio attempts to battle when he really mistakes Sebastian for Cesario who is still Viola in drag.
Feste is the clown who is really smart but dresses up as a priest and imprisons Malvolio for madness even though Malvolio is not mad. Feste also sings a lot.
Sir Toby and Sir Andrew are the two men who remain drunk the entire play. Sir Toby is Olivia’s uncle who marries Maria. Sir Andrew loves Olivia but doesn’t stand a chance between Cesario/Viola, Sebastian, and Orsino.
Antonio is the man who never admits it but really loves Sebastian. He rescues him from the shipwreck and goes with him to Orsino’s house which is where Viola is, in drag as Cesario.
Viola and Sebastian think each other dead. Antonio later mistakes Viola for Sebastian and gets his feeling hurt.
But don’t worry, this is a comedy, so everyone gets married and dances and sings at the end.