Instead of trying to organise a public event, this idea would see a well-briefed moderator interviewing each of the candidates; they would ask the same or similar questions and would give each candidate the same amount of time (say around 15 minutes). The interviews would be recorded at a time to suit the individual candidates. Once they have been recorded, they should be stitched into a single video then uploaded to YouTube, Vimeo, Facebook or another suitable platform, making sure each candidate is fairly presented, that they have all been able to answer the same questions and are all given the same amount of video time to speak.
The moderator would need to be prepared to think carefully about the questions and would need to ensure every candidate is represented fairly and accurately, and that no-one is getting more or less publicity. The coordination group would also need to put energy into ensuring publicity for the video is circulated widely.