If you want any free money from the school, such as scholarships or grants, or school-funded loans that have super low rates, then you have to do what the school asks. The school is not taking your word for it that the numbers you put down are correct. So you either pony up your tax return and your parents' tax return, or you refuse. Either or.
This happened in my family when I was a kid. My uncle was paranoid about releasing his tax returns, and my cousin couldn't go to Stanford, where she got accepted. She went to a community college and is a bank teller now.
Best of luck to you.