It shouldn't be too difficult. I don't know if you've seen the early access of Solasta, by a dev team of only 17 people, but it is another 5e based videogame very similar to BG3 in a lot of things, but seems to be doing things better in regards to gameplay. All custom characters are fully voiced and when you interact with NPCs each "option" of the dialogue is said by a different character according to their personality. Alignment and personality tags help shape what kind of things your character would say.
Generally when people talk about fully voiced they mean 'have personalities and backgrounds' and you can have conversations with them. Havent played the game but it sounds like they just talk when you give them an order like it is in bg1+2?
If not that does sound impressive.
