In context, the brothers
is most likely a reference to the Jews and Gentiles who were part of the synagogue. The Jews who are unwilling to believe that Jesus is the Christ do their best to prevent anyone within the synagogue community from listening to Paul. They also make plans to turn the minds of the larger Gentile population against the two missionaries.
2 Mais ceux des Juifs qui ne crurent point excitèrent et aigrirent les esprits des païens contre les frères.