Final answer:
The subject pronoun to use is 'Ellos' when talking about Mr. Echenique and his brother in Spanish.
Step-by-step explanation:
The subject pronoun that you would use to talk about Mr. Echenique and his brother is Ellos. This pronoun is used to refer to a group of men or a mixed group of men and women. For example, you could say 'Ellos son de la República Dominicana' to mean 'They are from the Dominican Republic'.
Learn more about Subject pronouns in Spanish