I’m not sure anyone is trying to game. I think grandma was confused in what she asked. She may have asked something as simple as, well, I house and feed these kids, OP pays next to nothing, whose financial info?
Fafsa confuses some of this. But they say this, for whose financial info is needed on the application:
“A legal parent includes a biological or adoptive parent, or a person that the state has determined to be your parent (for example, when a state allows another person’s name to be listed as a parent on a birth certificate). Grandparents, foster parents, legal guardians, older brothers or sisters, widowed stepparents, and aunts and uncles are not considered parents unless they have legally adopted you.”
OP is the parent, the person whose info is needed. My interpretation, from what little we know from OP. If there’s some twist, OP needs to say.