Also yes, Shadowheart is not even a person anymore at this point lol, just a tool the Sharran cult of BG uses to get the Gith artifact.
Always remember Shadowheart might be the player character.
And some scenes likely play out differently depending on if Shadowheart is an NPC or the protagonist.
This is a trickiest part yes. Because if Shadowheart is the player character, then having her being just a puppet is concerning.
Just like in DOS 2, there will probably be background cinematics for each origin characters, so we can learn more about their past and what happened to them. Cause I would feel it strange that playing as Gale, you have not a clear idea what Mystra means to him and how he got his artefact 'curse' in the first place.