FIFA 18 has brought back the guest functionality, which allows users to local co-op in FUT Online Seasons and FUT Online Draft. This feature was included in FIFA 17, but noticeably absent in this years game.
The server update has already been pushed for Xbox One, PlayStation 4 and PC fans, so you can start playing co-op immediately. Some on-screen elements, specifically in the match setup flow, will be added in a future title update.
Check out the detailed post here, to find out how you can add a guest in FUT Online Seasons and FUT Online Draft.