Macbeth knows that Birnam Wood is approaching and his end is near
No improvement to this sentence is necessary. It makes perfect sense on its own and sounds right. "Either" always takes an "or" else the word wouldn't make sense, as it's meant to contrast binary options.
eg.
I'm either going to eat food or drink water.
Answer: because you chose not to make yourself happy.
Explanation: and what i mean is to find things that make you happy.
B) Summarizing the text that the group has read
C) Sharing an idea, claim, or theory about the story
D) Asking other participants questions about what they feel
You probably want to focus on major points which would be the plot and what happens during it and touch up on minor topics in the story. Like secondary Characters and small details, you would need to be very critical and stern since it is a critique. Major focus points would be the basis of the critique while minor points can help to serve as supporting evidence.