two-years-younger brother
The truth is, I do indeed have a brother, a blonde-haired, hazel-eyed, two-years- younger brother.

Two-years-younger brother

Not two-year-younger brother, right?

Question

two-years-younger brother
The truth is, I do indeed have a brother, a blonde-haired, hazel-eyed, two-years- younger brother.

Two-years-younger brother

Not two-year-younger brother, right?

Answer

The truth is, I do indeed have a brother.  He has blonde hair and hazel eyes and he is two years younger than me.  
The truth is, I do indeed have a brother.  He has blonde hair and hazel eyes and we are two years apart.  He is younger.
The truth is,  I do indeed have a younger brother.  He has blonde hair and hazel eyes.  I am older by two years.