Final answer:
The correct form of the future tense for the irregular verb 'decir' is 'dirán'.
Step-by-step explanation:
The correct form of the irregular verb in the future tense for 'Emiliano y Manuel' is 'dirán' (accent mark on the 'a'). So the sentence should be: Emiliano y Manuel dirán a su nuevo jefe que tienen que cambiar los planes para su proyecto.
Learn more about Irregular verb conjugation in Spanish