THE ANSWER
The campaign supports solo play, up to four players online, and two-player split-screen on console. A twelve-player Horde Siege match consists of three squads of four; it is not evidence of a twelve-friend party lobby.
Plan the setup before the invitation
Kingy preparation advice · not a tested gameplay procedure
Use the planner to check the obvious limits. It flags too many campaign players, more than two couch players, PC split-screen and mixed-platform arrangements needing further verification.
- Count players, not controllers or consoles.
- Choose local split-screen or separate online devices.
- Check each player’s game access and, on console, the applicable online multiplayer entitlement.
- Agree a common unlock time and voice-chat method.
Compatibility still needs its own answer
The sources reviewed here do not establish a complete crossplay matrix, mixed local-and-online support, guest-account behavior or host/guest campaign-save rules. The planner does not mark those combinations as confirmed.
Retail menu-by-menu invitation instructions will be added after observing the shipping game.