the Doctor has never gone into any detail about any family he may have. Except for his granddaughter Susan, we don't even know if he really HAD a family. If the Doctor did have a brother, then he's never mentioned him before and will probably never mention him again.
So in short, no-one knows.
the Doctor did mention that he no longer had a brother, obviously believing him dead. But it is suggested that his brother may have been Braxietiel. Who he occasionally met in past incarnations, and once a colleague of Bernice Summerfield (a companion of the Seventh Doctor).