The correct form of the verb in the sentence is ahorraron. The tense is simple past because it is an action that happened the day before. Both words <em>‘ahorran’</em> and <em>‘ahorra’</em> do not refer to the past, and the word <em>‘ahorramos’</em> is in a plural form so it cannot be used.
The exact translation of the sentences is: 'yesterday, my brothers saved 25.000 pesos.'
