My Dad Has Stage 4 Cancer And My Mom Is Shutting Down

My(31F) dad(68) has stage 4 prostate cancer. A few days ago, he was rushed to the ER. They found some bleeding in his brain. The Dr's still aren't sure what's going on, but time is of the essence to get things sorted out. We have most things sorted like a will and death arrangements. Im currently my dads legal medical advocate because my mom(69) still hasn't signed the document, and im not sure if she ever will. My mom has been depressed and i understanding that makes things a lot harder, but she's neglecting so many responsibilities. She is medicated and has been for years, but he's worried that she will neglect her legal responsibilities once my dad passes away like Funeral arrangements, taking care of the house, selling the house if it comes to that, even just the basics of taking care of herself which she is already doing. She tends to stay in bed for long periods of time and not cook or bathe. She works very part time and even that is a lot for her. My dad was still doing all the cooking for her and my brother(28) and working full time up until last week. I also have a brother who lives with them who doesn't have a job or a drivers license. He's fully capable of having both but doesn't want to. He's also had professional mental health help for years. I’ve been trying to help as much as i can, but i can't take care of three adults; two of whom are fully capable of taking care of themselves. Basically, my dad was wondering if there was a way he could put me in charge of everything in the event my mom just won't do it. I love her, but she's just one of those people who won't listen no matter how many times you talk to her. My dad has worked so hard his entire life and also doesn't want my mom to just spend, spend, spend once he's gone. I dont want to take care of a house I don't even live in and the idea of having to try to control my moms spending habits with no real power is overwhelming. I have no idea what to do. Is there anything I can do legally that would protect my dad's assets from my mom if she continues her current habits? Any advice would be very appreciated. Thank you in advance. Location: Michigan