YOU SAID:

My younger, not older brother, ate my shorts.

INTO JAPANESE

兄ではなく、弟が私のショーツを食べました。

BACK INTO ENGLISH

My brother ate my shorts, not my brother.

INTO JAPANESE

兄ではなく、兄が私のショーツを食べました。

BACK INTO ENGLISH

My brother ate my shorts, not my brother.