This is a legal forum.
This is about legalities.
Your mother is NOT the child's Mom. Does your mother perhaps understand that she can be found to be alienating the child's parents? And that can be considered custodial interference?
You've received the legally accurate responses. Mom - THE REAL MOTHER - is not legally unfit, and your parents have no standing to file for any sort of guardianship.
Of course, if the parents - THE REAL PARENTS - agree, they can absolutely sign over guardianship (or even custody) themselves quite easily.