1. Yes
2. Yes
3. One
4. One has completely normal hearing.
5. One
Something about your project; your topic isn't that much of a question. If you want to win something, you need to choose a question that isn't answerable just by using common sense about how people lose their hearing and basic knowledge of genetics. You could go a lot further if you chose a topic such as "How do the HoH/deaf lose their hearing", conduct a survey on that, and a few other surveys such as "How were you educated?" "How were your parents educated?".
And just for the sake of political correctness, the term is Hard of Hearing or just deaf/Deaf. Although few people will take offense, hearing impaired implies that you think that there's something wrong with being deaf, that they're incomplete and have a tragic loss.
