Halsin should've been tadpoled, just like Minthara is. That'd already have helped making him fit in more as companion. Right now as it stands he's just that guy that suddenly wants to tag along for no reason except being horny for you and whoever you romance, he doesn't even like the city. His story inclusion ended at Moonrise Towers. Nightsong as paladin or Volo as a bard would've made just as much sense then. Volo could've even joined in act 1 already.
As for the other two, I still can't shake the feeling that Jaheira and Minsc having so much dialogue in act 3 is part of the reason that the rest of the companions feel so empty there (with the exception of Karlach who still, or almost only, has a decent amount to say in act 3). Opportunity cost and all that. I would've actually preferred if the Stone Lord was as much of an asshole as everything leading up to it leads you to believe. Even better if he weren't tadpoled, just a pure evil character that saw the chaos as a chance to try overthrow the more neutral Nine Finger.
