“Cash support.” (Can take many forms, but the usual implication is over and above the usual family relationships, small exchanges.) You don’t need to report grandma gave gas money, bought groceries, or paid for a dinner out. And if they live with her, she isn’t paying their rent. (Not “cash support.”) Sometimes, one has to interpret the intent of the questions Fafsa asks. A 529 is different, as is a 10k gift.
I do think some of the confusion comes from the "50% of the time, " which, for Fafsa, refers to unmarried, divorced or separated parents.