Household income?

Hi there so i'm applying for my maintenance loan, yes i know im just past the deadline but i got really confused on the application.
so im applying for both a tuition fee loan and a maintenance loan.
A bit of background i still speak to my parents but i live with my nan, im 18 so she isnt my legal guardian or anything.
When it came to filling in the details living with your grandparent isnt an option? so i put none of these apply to me.
However now they are asking for my mother and fathers details for my household income, but they arent by head of household, my nan is, who i live with? how does this work and why would my loan be based off people's income that i dont live with??