YOU SAID:

my sister is a cat so i am a cat too and y brother is a cat and were all cats

INTO JAPANESE

私の妹は猫なので私も猫で、兄弟は猫で、すべて猫でした

BACK INTO ENGLISH

My sister was a cat so I was a cat, my brothers were cats, they were all cats

INTO JAPANESE

私の妹は猫だったので私は猫でした、私の兄弟は猫でした、彼らはすべて猫でした

BACK INTO ENGLISH

I was a cat because my sister was a cat, my brother was a cat, they were all cats

INTO JAPANESE

私の妹は猫だったので私は猫だった、私の弟は猫だった、彼らはすべて猫だった

BACK INTO ENGLISH

I was a cat because my sister was a cat, my brother was a cat, they were all cats