I’m going to assume that it’s above board for now. I’ve seen situations where a family member takes in others and yes, that member is legitimately covering more than half the cost of the kids and hits all the marks to declare them as dependents. The parents could be house cleaning work which doesn’t require social security to be submitted; there are explanations and it’s not up to us to speculate on these things.
The bottom line is that the parents need to fill out the FAFSA for the OP to get a shot at financial aid. Without filed tax returns, a Verification Letter from the IRS is likely to be needed and to get one, ITINs are going to be needed. Getting all that from the IRS is going to take time so probably a good idea to get started. Also a good idea for parents to get a financial picture ready— gather those 2017 financials , get some blank paper FAFSA forms and start working on filling them out and have as much Verification as possible.