Your custodial parent is your dad. His legal residence sounds like it will be California...which isn’t going to help you with VA residency.
You need to find out your residency status for tuition purposes in VA. It is very very possible you will be viewed as an OOS student....with OOS costs to attend.
You need to figure out what you can afford to pay annually. Will your father be helping you with college costs? Your mother? For aid, you can count on a $6500 Direct Loan, and that is it. How will you find the remaining costs?
Your grandparents are not your legal guardians. Yes, you can live with them in VA, but this won’t help you establish VA residency to have instate tuition status. Your custodial parent lives in CA.
If you stayed in CA, would you have instate tuition status for the 2019-2020 academic year? Have you found that out?
But the biggest question is who is going to pay your college bills?? And how much can they pay.