Well at least one - Sam. But there are rumors that there will be a third Winchester(as in Dean having a second brother too), but we will find out the whole deal in episode Jump The Shark :D
He has two brothers,Sam and Adam. His father never told him nor Sam about their younger half brother. They met Adam and they later found out it was actually a ghoul when they went to a creepy house.Dean found Adam's and Adam's mother's body in two coffins in the basement,while Sam was being eatin by two ghouls (Adam and his mother are the disguise for the ghouls).Sam survived and Dean killed both ghouls.
Well, one that we actually give a shit about, but 2 technically. After I watched the episode where we find out Dean has another brother, I was really disappointed in John. I thought he loved Mary!
Dean has one living brother Sam & a 1/2 brother that was never revealed to them by their father. But he was later found dead in his house due to a Ghoul.
