system
Given the following post, respond as if you're commenting on Reddit:
human
[Batman] If Batman had a sibling, would they become a crime fighting duo?
gpt
Depends very much on the nature of their relationship and the sibling's capabilities, but overall, probably not.  

Firstly, the nature of their relationship.  Batman's descent into obsession (some would say *madness*) after his parents' deaths was partly due to the fact that he was now alone.  He had no one to help him through his grief and his sense of abandonment.  If Batman had a brother or sister he was close to, then it's quite possible that they'd be able to help each other come to terms with their parents dying.  In such a case, Batman would never exist in the first place.  On the other hand, if Batman was not close to his sibling, and they did not help each other through their grief, then it's possible he would still become Batman.  However, if they weren't close as children, then it's hard to imagine Batman trusting his brother or sister as an adult.  In such a case, Batman would still prefer to work alone.  

There's also a possibility that the siblings would turn against each other.  "Why didn't you do more to save mom and dad?"  In such an event, it's hard to say who'd be the hero and who'd be the villain.  It's possible there would be no heroes in this scenario.  

Additionally, there's no guarantee that a sibling would turn out to be as capable a crimefighter as Batman.  Sure, they'd share a lot of the same genes, but Batman's a one-in-a-billion crimefighting prodigy, in terms of both his mental and his physical capabilities.  So even if Batman would be willing to let his brother or sister join him on his crimefighting quest, it's up in the air whether the sibling would be up to the task.  Even if Batman accepts his sibling in a lesser role (such as a sidekick like Robin), if the sibling isn't up to the task of taking on supervillains like the Joker, then he or she might end up as a liability, to be used as bait or torture fodder against the Batman (see Jason Todd, Barbara Gordon, etc).  

So, on the whole, it seems rather unlikely for there to be Bat-siblings running around Gotham.