YOU SAID:

I once had a dream that my father was my mother and my mother was my sisted.

INTO JAPANESE

私はかつて私の父が私の母であり、私の母が私の姉妹であることを夢見ていました。

BACK INTO ENGLISH

I once dreamed that my father was my mother and my mother was my sister.

INTO JAPANESE

私はかつて私の父は私の母であり、私の母は私の姉妹であることを夢見ていました。

BACK INTO ENGLISH

I once dreamed that my father was my mother and my mother was my sister.