4. Do they speak casually or do they try to adorn their speech with frills? Do they maybe even dare to curse?
Mostly casually, unless she’s putting on a particular act. Lee’s the Personable One to Orin’s… whatever it is Orin is doing with her speech.
She doesn’t curse often, actually. She doesn’t have any objections to it, and is fine with taking Bhaal’s Name In Vain (as long as no one else tries it, only she is close enough to Bhaal to get that privilege) but is probably more likely to say fiddlesticks than fuck.
8. What was their relationship with Orin like? Did it change at some point?
Nightmarish! CW abusive relationships, incest.
They were always close, despite some competition between them (Lee was… Indulgent of Orin occasionally winning), and with the cult being The Way It Is, being close turned first into toxic codependency and then into “romance”. The relationship was never anywhere even approaching healthy, even leaving aside the whole incest thing, because these are people who think stabbing someone is a sign of affection and think boundaries are there to push at, but they loved each other in their own extremely twisted ways.
Lee… completely failed to see any change in their relationship. By the time the Absolute plot began, Orin was the most constant part of their life. Sure, playful murder attempts were fun, but Lee considered it understood between the two of them that neither of them could ever live without the other. She’d never leave them, so it didn’t matter if they pushed further than ever at her boundaries, if they were a bit colder or crueller than usual, if they were cancelling plans with her to be with Gortash instead.