You have two problems: the limited income (which raises their questions,) and how to explain the family support. And that you seem to have listed the grandparent money already, as a gift (or “something,” on FA paperwork?). On FA paperwork, that makes it look like either assets or theoretical “other” funds available to pay for college.
I’ll just say this as a starter, because a) this is common logic and b) yes, we get frozen when faced with this sort of task. I freaked at something I had to write and a savvy friend walked me through.
You phrase the grandparent money as what it is: support for living expenses. (Right? Not money for the college fund, not a discretionary windfall they gifted against, eg, your mortgage. Instead, money to help you month to month, right?)
You tell them roughly what it cost you for housing, food, etc. A defensible number. Presumably, you lived close to the line and the rough total of expenses you incurred and the total you lived on are close. You can say this was treated as interim help, that your intentions were/are to pay them back. You don’t have loan papers, nothing like a notarization or filing to support that, but it’s fine to say.
You note one bill was forgiven (1099,) a one-time event, necessary to reduce expenses, that you hope this will not be counted as on-going income. (Side note: 1099 IS treated as ordinary income, is taxable.)
You want this to be concise, so they can follow. Stick to the needed facts, don’t frustrate them with more detail and explanations than are relevant. State clearly and nicely that, if they need more info, you’re happy to provide it.
You have no control over how they react.
The next logical question will be: and then what? How did 2016 turn out?