Since all the Divinity-games had a free skill-system and we probably will get a chance to reset old skillpoints (like the demon in the D:OS), I don't really see a problem gameplaywise.
I know the option existed (and will likely be added again, as many people seem to cry if they cannot respec their characters at least once), but I usually avoid it. Simply doesn't feel right that Basil our muscular fighter with his backstory of singlehandedly beating a gang of trolls into pulp should suddenly be a nimble and agile marksman with otherwise unchanged origin.
I already said my piece about possible conflicts in the prisoner group and I still think, that there is enough room for interesting conflicts in the group.
No doubts here. I'm not saying that anything is wrong with a group of prisoners from a pure story perspective. There are endless backstories and possibilies for party interaction, regardless where you pick up your companions. From all the info we have, I'm confident that Larian will come up with handcrafted and elaborate story arcs for each companion. With multiple outcomes even, since we got the love & hate stretch goal.
I can only repeat myself: the narrative is not my concern at all. But for a good SP experience it takes a bit more than greatly written companions. They also need to fit in gameplay wise. And usually, party based RPGs allow picking the companions that fit to my gameplay style, and don't pin me down on my initial choice.
Still: What is more realistic? Travelling with persons you already knew from your days as a prisoner or a random Joe from the sidewald, who could be an agent or assassin? Doesn't help, that you could ask yourself about the other prisoners.
Well, in all prototype gameplay I watched, I did not see the players keep a low profile or show distrust to random NPCs. They were freely talking to them, doing their quests and errands, etc. ...
I don't see it as unrealistic or even far-fetched if one or two of those NPCs would turn out to be a potential companion.
Whether they turn out allies or enemies in the end is another thing entirely. Even your fellow prisoners may have a nasty surprise in store for you, depending on the way you treat them over the course of the game.