Universal credit and student finance.

Hi there. I am 19 applying for uni and have got most of the things set up. The only thing Is my parents can't do their part of my student finance application because they don't know Their exact yearly income. They are both on universal credit and unemployed so my question is can they write down a number based on the average number online (2 adults unemployed with children) or do they need the exact figure. Deadline is next month and it is making me anxious.