It's actually perfectly possible to make that work. See BG2 Jaheira and the Harpers incident. If you play a certain way, Jaheira WILL join the fight against you (And given her skill selection in THAT fight, this can be absolutely crippling too, especially when you do that quest late-game). Attack children on the street, and the paladin will openly attack you right then and there.
My point for bringing this up, the huge exposition dump this kind of design requires (select companions "front-loaded" at the beginning of the game) aside, is that I don't see how the game can be immersive when I travel as a "group" but every single character acts as a standalone entity. In BG2, when your *party leader* gained entry, the *party* was allowed in. This is why you call BG a "party based CRPG"
And this is what confuses the heck out of me. Are we playing a PARTY of people, 1 designed by us, up to 3 chosen at the start as companions. Or are we playing a mob of 4 people who we have to talk with 4 different times in every dialog ?
Or better put. Are companions actually integrated as part of the party, do they banter amongst themselves? Or are they just traveling along, but technically they are all stand-alone puppets who might at certain trigger points do X no matter how the travels, dialogs etc went?
Hmmm, yes this is probably trickier than I realized (though defecting companions is actually simpler than I thought). I don't think there's anything wrong with talking to people with each character and getting different options. Might be a little tedious by yourself, but it'll definitely be immersive when an NPC addresses each person differently. As far as I can tell, you have your own main character, and you can choose your three companions at the start, apparently not being allowed to choose the companion that has your origin. I certainly hope you'll be able to influence your companions, set up agreements like you can with multiple players, so that they don't just do X at a certain trigger point, but could do X, Y, or Z depending on your previous interactions. Lots and lots of work to pull that off though.
What will be somewhat awkward is when say, you're trying to get in that town, and one of your characters (say, the dwarf) can't get in, so you have to spend a while getting that character in while your other characters do nothing. I don't think that's too problematic though, and there were situations like that in D:OS too. I'm not expecting that the other companions will just wander off and do their own thing while you're controlling the dwarf, though that would be totally epic in a certain way. Kind of like GTAV, where you control one character at a time, and if you switch back to other characters, they'll be in various (mostly comical) situations. That would be seriously next-gen stuff if they could pull it off in D:OS2, but it's hard to imagine it actually happening.