Your parents being unwilling to fill out the FAFSA will really penalize you as you won’t be eligible for Pell grants, SEOG, some state grants, and sometimes even grants or scholarship offered through the school.
You might be better off becoming a ward of the state. You never have to go into physical custody, but if the state becomes your legal guardian before you become 18, you will be eligible to file FAFSA as an independent. The paperwork will be easier as you go through college. It may have been better for your grandmother to take you into her house, but you might get better benefits if you become a ward of the state, live with your grandmother, and get to file taxes and FAFSA as an independent.