I don't think Haslin is confirmed, but he does have dialog that says that he wants to go with you to the towers and he ends up at your camp after you rescue him. So, yeah, I'm like 99.9% positive he's in. Karlach says that she can't join until you reach Baldur's Gate, so she's probably a Act 2 companion.
I was seriously considering playing my MC as a Druid, and I still might, but I am enjoying playing as a Sorcerer more than i anticipated so I might go that route. However, after starting the thread about how to play Wyll as a Warlock, I'm sorta intrigued about trying out that class since I don't particularly like the Wyll character.
