You cannot claim expenses for something you haven't paid for. If you were paying rent to your parents, you might be able to claim the portion of your rent that relates to your home office.
If CRA request proof of your "Business Use of Home" expenses and you could provide receipts showing that you had actually paid these bills, your claim would be disallowed.
Here's a little more info on claiming Home Office Deductions: https://bit.ly/2HfwRPy