Where Do I Begin With Getting Custody Of My Younger Sibling?

Location: Michigan.

Some background:
My youngest sibling is 15, she lives with my mom (46) and her dad (47), who is loosely like a step-dad to me. Since buying a house three years ago, I've been low contact with my mom and step-dad due to abuse/neglect that I experienced in childhood, really only keeping minimal contact to interact with my sister and her older brother (22).

Last month I was alerted to the fact that my parents had received an eviction notice and had to find a new home by the end of August. They're still in their current home, but got approved for an apartment somehow. My mother hasn't worked since 2004 and my step-dad has never worked a job that wasn't under the table and rarely got paid for his work. They rarely have the funds to make ends meet due to their legal drug habits and poor decision making, between the ages of 9 and 18 (when I moved out) they had a functioning vehicle for maybe a collective of a year and a half. Currently they don't have a functioning vehicle.

Now that I'm 25 and live in a house with a steady job, I've been preparing to take in my sister when she turned 16. However, with the eviction, I was prepared to take her in last month if it came down to it. With my parents moving into a two bedroom apartment, my sister no longer has a room of her own. I believe that my parents are unfit to take care of her, and she won't have as many opportunities if she stays there.

She's a sophomore in high school and can barely read, perhaps having closer to a late elementary school reading level. She's talked to me about dropping out, she wants to move in with my partner and I because the stress added by their inability to keep manageable funds has taken a toll on not only her parents relationship but her mental health as well. I know she'd have a better quality of life with me, her own room and I'd carve out time every day to help her with homework. My partner and I plan to get her into drivers training so that she doesn't have to struggle getting her license as much as I have.

My question comes here:
From everything I've seen doing research online, it looks like the only way I could get guardianship or custody of her is through probate court and her parents have to be willing. Her parents are unwilling to give up custody of her. What are my options to try to get custody of her? I've reached out to a lawyer about a free consultation with the gist of my problem but haven't heard back yet.

I want to take the steps to give her a better life, but struggling through legalese hasn't bore any fruit.