In the game, each NPC has an attitude score.
But will the Baldur's Gate 3 have a shared party reputation system like in the BG 1,2?
Not like in Bg1 and 2 - thank God. Your reputation is a lot more nuanced in Bg3 - for one you are judged more as an individual and while you may garner suspicion if another party member steals it won't directly affect your reputation.
For example: We all have a reputation with each individual NPC that can be affected in various ways (its a literal bar that you can see on the trade screen on the bottom right corner that goes from Red, Orange, yellow, Green). If you GIVE gold and items to traders it will increase your rep but only for that party member - which will result in lower prices - but ONLY for that party member.
I have seen ACTIONS also affecting that reputation score, such as hiding, sneaking about, stealing and being caught, murdering random people in view of other NPC's.
If your reputation drops too low with specific NPC's then they will be unfriendly to you and may become hostile but you are given the chance to make it up to them with Gold or items.
There is also faction reputation which does actually usually affect the entire party. However factions are NOT explicitly spelled out, but seem to be a tag that is behind the scenes.
For example: Killing the Goblins in the blighted Village doesn't make the Goblins at the Goblin Village or shattered sanctum hostile - it doesn't even make the Goblins at the Windmill hostile - which is IN the Blighted Village.
I am excited to see how this all has evolved in the full game.
Honestly the reputation system in BG1 was my biggest problem with it. It literally made no sense.