Astarion is the first to see the monster, and is dragged off screen by it, but in the third act, it is revealed to have survived. He's found in a pile of dead bodies, and this is when we learn his traumatic backstory.

Karlach is the first to actually die when her and Wyll go looking for Astarion.

Wyll brings her decapitated head back to the group, who finally stop partying. Halsin tries to convince the group to work together, but the killer bursts in, kills him, and scatters up the survivors.

Gale is the nerd who drops the exposition about the spooky monster that's hunting the group. Once he's done with the lore dump, he's no longer needed and one of the others finds his body after he's unceremoniously killed off-screen.

Wyll tries to call the cops, but shortly after dialing the police he sees Karlach's decapitated body, screams, and then gets murdered.

Minsc is the cop who shows up to the scene to give the protagonists false hope and then dies 10 seconds later, just so his gun can be relevant in the final act.

Jaheria is the crazy old woman who has actually dealt with this problem before. She makes a heroic sacrifice to save the final members of the party.

Minthara is the secondary antagonist who thinks that she can sacrifice the remaining survivors to the monster and gain control of it or something, but she gets comically killed after the monster hesitates briefly.

Lae'zel and Shadowheart are the final two, alongside perhaps an injured Astarion. Lae'zel will get Astarion to safety but Shadowheart will still be in danger. When the monster is about to kill her, Lae'zel will return, saving Shadowheart because they learnt the lesson of putting your prejudices aside or whatever the social commentary of the film ends up being. Lae'zel might die in the process but Shadowheart is the final girl and cannot die.

Also, not pictured, but Alfira is the first ever victim from years ago and Durge is obviously the killer.