Only Moderators and Admins can add polls to an exsisting topic. In future, report a post within your gang's topic and make a request. I have gone to the liberty of contacting a member of staff, so that this poll can be added to your gang's topic.
As for your question, we would only allow it if you keep this branch within the same topic as your current one. For the most part gangs' members and hosts are not allowed to create multiple topics surrounding one gang/event/alliance, let alone multiple gangs.