"Each dart hits a creature of your choice that you can see within range."
If you can see an enemy creature, then magic missile can hit the creature automatically because no attack roll or saving throw is mentioned. And because 5e doesn't care about body parts, seeing even a fingernail means that you can hit them for full magic missile damage.
If you hover over an enemy and BG3 tells you there's a valid path (direct, non-curving line-of-sight) between you and the enemy for the first missile to travel along, then all missiles should hit. You shouldn't have to find a valid body party where 3 missiles can take different paths and all hit.
