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.
I used a build, Wolfheart recommended in one of his Videos: the Sorlock. Play sorcerer and at level 4 select the fest Nähe Initiate Warlock ( and of course the spells Hex and Eldritch Bläst). It is really fun so far and a bit like multiclassing. This way, you can have the sorcerer class with warlock spells.
Äldritch Bläst!
That was my spellcheck --- and I'm not sure, how it made Bläst out of Blast, but it is funny
Do you have say, Swedish in your keyboard languages? Because my autocorrect loves to autocorrect to Swedish sometimes... And it would certainly fill in blästa because it's part of my address.... >< and I use it all the time.