Fortnite received an update today that introduces local split-screen multiplayer for Duos and Squads. The feature is currently only available on the PS4 and Xbox One. A few other features have been added as well, including a change to the visual representation of remaining ammo and preparations for the upcoming Star Wars: The Rise of Skywalker live event.
https://www.notebookcheck.net/Local-split-screen-co-op-comes-to-Fortnite-on-PlayStation-4-and-Xbox-One.447145.0.html