I'm sorry to hear about your uncle and for its impact on your family. I think it's likely your uncle has a gut feeling about how much time he has left and is trying to live as normally as possible. If you aren't seeing a therapist, please seek one out to help you through this. Spend as much quality time as you can with your uncle so you have those happy memories to fall back on.

My father died of brain cancer in 2002. It was hard on the family. I know some of how you're feeling. Please continue to post here if it helps. Best wishes.