I eared somewhere that Divinity accept local turn by turn, i.e. players away from the combat are not in turn by turn.
You heard? As in, you haven't played D:OS 1 yourself? I mean, what you heard is true, but if you haven't actually played D:OS yourself, you might be carrying in some assumptions about the game which can lead you to make some incorrect assumptions.
Without modding, D:OS has no day/night cycles, NPC schedules, no enemy respawning, no resource respawning. I'm not sure that there will be enough things to do in the world to keep player interest without pretty frequent content injections by the GM.
The hard limit on players is an engine limitation, I believe. I don't think it can handle more than maybe eight or so players at the absolute most, and there is only one party. You don't have to stay with the party, but all PC's portraits will be on the screen, so there isn't really such a thing as two different parties, never mind enough players to require more than one GM.
There are resurrection scrolls in D:OS so a dead player can be brought back.
If you haven't played D:OS, you really should play it to get an idea of what it's like to adjust your expectations.