Final answer:
The pronoun that completes both sentences is 'les'
Step-by-step explanation:
The pronoun that correctly completes both sentences is les.
In the first sentence, the verb gusta is used, which agrees with the third-person plural pronoun les when referring to 'your brothers'. So in the first blank, we use les. In the second sentence, the negative form no les gustan is used, which also agrees with the third-person plural pronoun les. Therefore, in the second blank, we use les.
Learn more about Spanish pronouns