If you have an idea of the likely audience, pitch the questions at them eg if most are over 60 they are unlikely to know a lot about current pop music so will think those are hard.
Ask someone to help you set the questions or act as the audience (someone who won't be at the quiz night) - if they think questions are hard then reword them.
Be aware of possible alternative answers and decide if you will accept them - British Prime Minister in 1940 could be Chamberlain or Churchill
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Remember the reason for the quiz is to raise funds for your charity. If those there enjoy it they'll come to another, if they don't they won't
Hope these help