Grandparent 529 withdrawal question?

My son will be a junior in college. The grandparents have offered to contribute to tuition for the next 2 years with 529 funds they have saved. How do we do this without impacting future financial aid?

When we have paid from our 529 we do a direct transfer from the 529 to the university. If the grandparents do that won't the school know that the student received grandparent help and then reduce the aid received next year? 50% is what I've seen listed (ie: if grandparents give $10k, next years package is reduced by $5k)

I think they could transfer money to my son as beneficiary. Does he then need to pay the tuition bill? Or could my son then transfer to us and we pay the bill. (read: would it be a red flag to financial aid that a student has 10k to put towards tuition?)

Thanks for any guidance.