Keep a separate file for each grandchild student who is a 529 beneficiary. With just a little bit of organizational skills, keeping up with three shouldn't be any more difficult than keeping up with one (which is pretty easy).
If you have the 529 plan administrator send the funds directly to the school for direct billed qualified expenses, the 1099-Q tax form that comes from the 529 plan will be issued in the student's name and SSN. That means that any "tax problems" will belong to the student and not you as the account owner. Make sure the student knows that any refund of expenses paid with 529 funds can be recontributed to the 529 within 60 days of the date of refund, without any penalty or tax consequence.
Off-campus qualified room and board expenses add a twist, but again, even a modicum of organizational skills is all you need. Just make sure not to use more 529 money than the school's published cost of attendance for the student's particular situation, and as always match up the 529 distributions and the actual payment for the expenses that are being covered in the same tax year.