YOU SAID:

My dad told my sister that he had never told her mom who was the guy who betrayed her.

INTO JAPANESE

私の父は妹に、彼女を裏切った男である母親には決して言ったことがないと言った。

BACK INTO ENGLISH

My father told his sister that he had never told his mother, the man who betrayed her.

INTO JAPANESE

父は妹に、母を裏切った母親には一度も言ったことがないと言った。

BACK INTO ENGLISH

The father told his sister that he had never told his mother who betrayed her mother.

INTO JAPANESE

父親は妹に、母親を裏切った母親には一度も言ったことがないと言った。

BACK INTO ENGLISH

The father told his sister that he had never told his mother who betrayed her mother.