No. There is no story about the joker that reaches that far back. There are very few that even touch on the topic of his creation. So yeah.... id assume no. It seems to me that jokers insanity is more nurture than nature, meaning its his environment that changed him and made him crazy so even if he had a brother, there's no telling what he'd be like.
And side note. Dude u think dexter season 1 is good. Keep watching. All the way to up to date. Pm me if you have any trouble getting your hands on it.