“My parents have accounts (one each) where their wages are deposited, but it is not the kind of deposit where you get an interest on your amount of money, it exists just so they won’t have to take their wages directly at hand”
This is exactly what the school is looking for. The school is looking to see documentation of income (the wages getting deposited) and the assets (the total balance). They are not concerned about interest. Do your banks not provide a monthly record of the account like ours do? Are they able to create one if you asked?