Leigh Brackett = I’m 99% sure it’s “Lee”. Leigh is quite a common name and it’s always prounced this way in my experience.

Richard Marquand = It’s pronounced as it’s written with the Q. “Mark-Wand”.

“Kaz-AN-jee-an”? = Correct. Although the “Jee-an” would probably roll off the tongue as just “Jan”.

Ian McDiarmid = It’s “Muck-Dear-Mid” from all the times I’ve heard it said. “Mc” is sometimes pronounced “Mac” (Like with my name) but in this case it’s “Muc”.