You won't have to do them, but those will be the moments Laezel expresses herself as Laezel. Not doing them is an option but also doesn't fit with the person you're trying to play as. Playing against them at every turn is unsatisfying in DOS2 and I'd expect the same here. You can sand down the edges but the core remains the same.
That's not really how I read her. She's from a harsh culture, but also rather naive. We haven't seen the Githyanki yet, but I suspect somehting terrible will happen there that your Laezel can go with, or against. Either will 'feel fine' and develop her path from there. Kicking kittens is on you, but not really how I read the character; she's more pragmatic than purely evil. Making fun of Dwarves is, though. I'll grant you that.
Shadowheart is lying about who she is. At the start of EA she wasn't competent at it but after refinements she's got some semblance of manipulation going. If you're not seeing her as full on stupid evil then that shows the manipulation is working.
Her story is that she's a spy whose memory was wiped by the Sharrans. Now, she may or may not suspect that, but not saying who she really is, isn;t exactly lying either. She's not very trusting, as befits both a spy and a Sharran; but shes conflicted more than most when taking the evil path, so, her actual heart might not be all that shadowy.
Karlach is a closed book but all the other origin characters are evil I can't imagine she's an exception. There's going to be some very grim stuff in her backstory for sure and much of that is still bubbling along.
Probably, but she's also the one that wants to go out on dates and discuss marriage and children and such. Again, I think it'll feel natural going either way. I can see her slaughter hundreds in a fit of rage when betrayed or pushed too far, too. I think this is the one most tailored to modern audiences.
I genuinely think you should approach it differently; instead of picking Paragon or Renegade just for the colors - Try and pick what feels most natural to you and your character. Who benefits in my party? Who do I trust? It'll make for a far better experience, regardless of who you play. They said in one video or another that no playthrough is truly good, and no playthrough is truly evil. Although the Urge might have something to say about that.
What frustrates me more is while all of this makes it hard to embody any of the female characters in BG3 the guys fetishising lesbians have at least three conventionally attractive options.
Yes, well. It's the same options you have.