Question

not only my father but also my mother is a teacher.还是not only my father but also my mother are

not only my father but also my mother is a teacher.还是not only my father but also my mother are teachers?

还是这两句都不对？求答

如果改成用Both来怎么说呢？

Answer 1

not only my father but also my mother is a teacher.是正确的。
not only....but also这个短语采用“就近原则”，即谓语动词用单数还是复数，取决于离谓语动词最近的名词。这个句子中，离be动词（is）最近的是my mother, 为单数，所以be选择用is。
例如：not only you but also his parents like swimming. (离谓语动词like最近的是his parents, 谓语动词用单数形式like，而不用加s)

both意思为“两者都是”，即主语为复数，则谓语动词要用复数形式。
both my father and mother are teachers.

Answer 2

not only my father but also my mother is a teacher.
Both my father and my mother are teachers。