How do I teach teenagers about faraid so they do not fight over property later?

Teach faraid as Allah's justice and a family trust, not as a list of who gets how much. Teenagers accept it more easily when they understand the reasons. Explain, for example, that the male share is larger because of his duty of maintenance (nafkah), and that elderly parents are also entitled. More importantly, set an example: how you yourself handle the family estate honestly, and how you forgive relatives who make mistakes. Also tell stories of families torn apart over property as a lesson, without naming names. The Prophet ﷺ said: “Do not envy one another, … do not hate one another, … be servants of Allah, as brothers” (Sahih Muslim, Kitab al-Birr wa as-Silah wa al-Adab). See educating the family.