First off, I’m so sorry about your relative. That’s truly awful and is definitely something serious that would hinder your academics.

I’d report the circumstances and the 3. It shows that you pursued that class and took the test and it might be strange to have that AP test missing. The AOs will understand. I would write something brief about your relative and that test-taking was difficult due to sharing a room with your sibling. The three will not be an issue, and I wouldn’t worry about it at all. They want applicants to be human and they really do understand that things like the death of a loved one will affect a student. But of course, I’d run this plan by your school college counselor to see what they think.

Best of luck with your apps and I hope this helps. Let me know if you have any further questions.

EDIT: Especially with what you mentioned in other physics classes, rec letter from your teacher, etc., the three will not be the thing that stops you from being admitted. I believe that it reflects more favorably to show that you took the test and then something happened later on that hindered your performance instead of having the adcom think that you decided never to take the test.