Whether the grandparents ts put the money onto a 529 or into your checking acount makes no difference. If there is a question about receiving gifts you list it, if there is no question you dont. It is not income, it is a gift. If the money is IN the account when you report it will be assessed at 5.6% but it is is not there it will not be assessed at all. If there is a question about gifts, the school will consider it as they deem appropriate. If it is $30k, yes, they probably will consider it.
Again, how much do you expect in need based aid if the grandparent contribution is excluded from the picture?
The financial aid office is not tracking your assets or income or gifts. If there is a big change in reported income, you will probably be selected for verification. Most of the financial aid documents are self reporting. If you don’t report something, they won’t know. I have a small bank account at a credit union because I have a credit card at that credit union. I failed to report this $50 on fafsa the first year. As we got no financial aid at all, it didn’t matter, but no revenue agents came to the door wondering why I hadn’t included it.