How do i say goodbye my brother in japanese'?

That would be 'Sayonara Nii-san' if they are older. There are many different ways to say older brother, I chose nii-san since I believe it to be the most common.

If it is a younger brother one would say 'Sayonara Otouto'

Both of these simply read 'Goodbye Brother' because in Japanese Words like my are understood.