Group play is a paid-tier feature for the host; friends join free from their own devices. Host a game to get a 6-character invite code; players join at the join screen, build their heroes, and ready up. When everyone's ready, the host launches.
Out of combat, the DM waits for every player to act before responding — one narration per party round, so nobody's action gets skipped. In combat, initiative order rules and only the current player may act. If someone closes their tab, a notification nudges them when the table is waiting on them.