1J

What do you think Quillian meant by men in glasshouses shouldn’t throw stones? Could this be connected to his visit to where he was murdered?

Quillian knows something that the Bishop or his family was/is involved with and his warning him to stay out of the slavery fight or he may expose him. I do think it's connected - there's something that happened in the past that's resulted in this murder.

We've heard about 3 of the Bishop's brothers, I think - what about the 4th?

Too many people know how the Bishop felt about the slavery issue so he needed to be very careful what he said and to whom he said it. Wasn't there 5 sons? If that's right then the Bishop has 2 brothers that haven't shown up yet.

Quillian seems to think the Bishop was murdered for something he said.

I think Quillian know something about his past. I don't know what it could be but likely it's connected to the 1st murder.

I couldn't quite work out the reference. Did his family have slaves at one time? Or perhaps Brenda is on to something, and the other brother owns a plantation somewhere...?

I agree with >2 bhabeck:. There's something from the past that caused the murder.