What does Antonio learn from his brothers and the boys at school about how to become a man? Why might they be incomplete models for him?

This is rather involved and explained thoroughly in Gradesaver's analysis for this section. Follow the link provided below and feel free to ask further specific questions you might have.

http://www.gradesaver.com/bless-me-ultima/study-guide/summary-chapters-8-10-ocho-diez