Not real sure, but I think it's because of 1. They discouraged fighting for the fear of Tybalt's certain exile. And 2. It was a party, "So let Romeo alone to his fun and party! For what harm?"
The answer for this question is B
THe answer is A. Themselves. A reflexive pronoun indicates that the person who is realizing the action of the verb is also the recipient of the action.
