Clearly between C and E.
(C) whether the movie should be classified as a murder mysteryYes, I think this is the correct one. First person clearly states that it is a requirement of murder mysteries that viewers be given clues to solve the mysteries. This first person thinks that the movie is indeed a murder mystery.
Second person, on the other hand, states that the filmmaker wanted to keep the murder thing as a side thing and his primary focus was something else. Clearly, in the second person's opinion, the movie is not a murder mystery as murder is a side element in the story.
(E) whether the filmmaker wanted viewers to be able to solve the murderWrong in my opinion.
First person simply states what are pre-requisites of a murder mystery. She never talks or implies that filmmaker "wanted" the viewers to be able to solve the mystery. So she cannot disagree with the second person on this topic.
Second person, on other hand, clearly believes that filmmaker does not want to divert any attention to murder stuff, and that murder element is just a secondary thing.
I welcome any comments on my reasoning

Appreciate Kudos if it helps xD
Regards,
Saakhi
C couldn't be the answer, I am just going with your reasoning of C.
"First-person clearly states that it is a requirement of murder mysteries that viewers be given clues to solve the mysteries. This first-person thinks that the movie is indeed a murder mystery."
So it means that First-person states that a movie cannot be classified as a Murder mystery. Clear logic.
But for 2nd person, he states that the Filmmaker wants us to focus on something else rather than the murder mystery. According to the second person, the movie could be a murder mystery/ couldn't be a murder mystery, it didn't tell us anything. In fact, if you can still assume for 2nd person as well that he didn't regard this movie as a murder mystery.
So both 1st and 2nd person basically just agree on C. But we have to find on which they disagree.