Michigan — My Sister Is Profoundly Incapacitated And Has Never Actually Cared For Her Autistic 12-year-old. Can My Parents Obtain Custody/guardianship?

Location: Michigan.
I want to understand what options my parents may have and what we should be asking for.
My 12-year-old nephew is autistic. His mother (my sister) has technically had legal custody of him, but she has never actually functioned as his parent.
For essentially his entire life, my parents have been the ones raising him. My sister lived in my parents’ home with him, but she did not care for him, take him to school or appointments, manage his needs, etc. She essentially used the fact that she had legal custody as leverage to prevent my parents from making her leave the home. In practice, my mother has been his caregiver and has handled his day-to-day life, including taking him to school, medical appointments, and presumably managing his other needs.
His biological father has been even less involved. He has essentially never been in the child's life and does not know his son. He has a history of drug abuse. As far as we know, he has not been involved in raising, supporting, or caring for the child.
Nine days ago, my sister was hospitalized after a catastrophic medical event. She is now profoundly incapacitated. She cannot speak, communicate meaningfully, move appropriately, eat independently, make decisions, or function independently in any way. She has been this way for over nine days. She is currently unable to communicate her wishes regarding her son or make any decisions for him.
The hospital has not declared her permanently disabled or permanently incapacitated. We obviously don't know what her ultimate neurological outcome will be, but at this point she is completely unable to exercise her parental responsibilities.
My parents are now extremely concerned about my nephew's legal situation.
They want my mother to have legal custody/guardianship of him because she has effectively raised him his entire life, and she is the person he has relied on for his actual care. They are worried that if my sister remains legally incapacitated without any formal custody/guardianship arrangement, his biological father could suddenly assert his parental rights and attempt to take him despite having essentially no relationship with him.
There is also a concern that my mother may eventually pursue legal action against the hospital regarding my sister's care. We are worried that if there were potentially significant damages involved, the biological father could suddenly become interested in the child for financial reasons. We obviously cannot prove his motives, but given his complete lack of involvement until now, this is a serious concern for my family.

Our questions are:
Can my mother petition for temporary or emergency guardianship/custody of my nephew while his mother is currently incapacitated, even though the hospital has not declared my sister permanently disabled?

Can she pursue full guardianship now, or does my sister first have to be legally declared incompetent/permanently incapacitated?

Does the fact that my mother has been the child's actual caregiver for his entire life give her standing or otherwise help her case?

How much weight would the court give the fact that his biological father has essentially never been involved in his life?

Is there anything my parents should file immediately to prevent the father from suddenly taking the child while this is being sorted out?

Would this generally be handled through Michigan probate court (minor guardianship), family court (custody), or potentially both depending on the existing orders?

What documentation should my mother start gathering to prove that she has actually been this child's primary caregiver for his entire life?

We are trying to protect a 12-year-old child and maintain the stable caregiving arrangement he has always had while his mother is currently incapable of making decisions.
I understand that this is complicated and that we need an attorney. I'm mainly trying to understand what type of emergency/temporary legal protection we should be asking for and whether my mother's long-standing role as his actual caregiver matters legally.