Our district council PTA usually has the League of Women Voters ran these sorts of events. The League provides a moderator who comes prepared with questions.
I wish there was an opportunity for audience members to present questions. If I were doing that, I would have them presented to the moderator as suggestions. Then, I would allow the moderator to select the questions they thought best, and rephrase them as necessary to remove bias. "In light of projected budgetary shortfalls, how should the district handle funding for extracurricular activities?" as opposed to "what do you think of candidate Johnson's chowderheaded 'pay-to-play' suggestion?"
Last cycle, candidates were grouped by the seat they were running for, and then randomly assigned seats. They then randomly chose the candidate to be first to answer the first question, and went in turn around the table; the candidate who answered second was the first to answer the next question.
What they didn't do was reverse the answering order after going around once. That meant that one candidate got to answer after hearing their opponents answer on all but one question. On that one question, the opponent answered later but only after all other candidates had spoken.
Final thought: opening statements, answers, closing statements -- set a time limit and hold them to it. Have a timekeeper. When the candidate has 30 seconds left, have them give some clear signal such as holding up a colored card. When their time is up, if they are still speaking the timekeeper should ring a bell or otherwise disrupt their speech. If you have microphones and a sound board, be prepared to hit the mute button if they keep talking.
I organized one of these a couple of years ago. First I nailed down the date and location, then I sent out invitations to the candidates, explaining the set-up, which was: First, a statement they would prepare ahead of time to introduce themselves and their backgroud, experience - I gave them about 3 minues each for that. Prepared questions by moderator - 3 minute answer time by each candidates and then the last 15 minutes for questions from the audience. I invited the local newspaper and advertised in a weekly freebie newspaper. Sent flyers home through the elementary and middle school - it's hard to get things through the high school. Anyway, it wasn't well attended but the candidates were there and I felt good about doing it. good luck!
Our PTO is having a "Meet the Candidates" night in order for the parents to meet the candidates running for the Board of Education. I need any/and all suggestions that you each may have regarding running an event like this. ASAP please, it's coming up fast. Thanks.