The whole point of our group is the imminent thread from the tadpoles. I think that is a good way to get people so different to work together.
And even so, I actually killed Astarion a few times in EA, because he attacked me unprovoked. I still need a very nice chatacter to let him go away with it. Lae'zel is not friendly, but she is practical and honest with you from the beginning. Still, without the tadpole threat and knowing about githyanki, I would probably leave her alone.
I think Shadow revealing who she is, is a big deal too. She serves one of the most evil goddesses, who demands vile things of her followers, that is hard to swallow. By the time, she reveals it, my character is usually already on good terms with her, but it still is a lot.
I think without the tadpole reason, my characters would not necessarily team up with Lae'zel and Karlach and might have trouble, trusting Shadow after her reveal. That would leave Wyll, Karlach, Jaheira and Minsc. Halsin would be kicked out, for being an annoying sex maniac.
And so you would have a choice of who you want to take with you, my choice would be different, I'd probably keep Lae'zel to tag along, same with both Wyll and Karlach after clearing up the entire situation, which if you just hear Karlach out and do some quick research is pretty easy. I'd be way more inclined to tell Gale to piss off if it weren't for our mutual crisis, too, but I know others wouldn't, given he is a very kind person.
I don't know if you intended it, but you proved my point exactly, even without the imminent threat, I think it's possible to form a group of unlikely allies.
