His father and my teacherteaches French.
请问这个句子的 teaches 用得对吗？为何不需要 teach 呢？
His father and my teacher teaches French.
一般不会如此说。你的句子要想理解为理解的句子，只有一种可能，就是将 His father and my teacher 理解为“并列同位”结构，即属并列结构，但表同位关系，即 His fatherand my teacher 指同一个人，句意：他的爸爸也就是我的老师是教法语的。
假如要理解为两个人，需要用复数动词 teach。