As @FangxiaL stated if the only source of income your parents have is social security they do not have to file a tax return. If they do have to file a return when you answer the question for the Economic Impact Payment you would need to enter the amount of $1,400 in each box. If you leave it blank it will not let your complete the return. If you answer "0" in each box it will cause a credit that will create a refund. You have to enter $1,400 for each. This should not create a tax for them, as there the Economic Impact Payments are not taxable.
