When my mom's health was declining, beginning at about the age of 80, I had to be the one to step up and take care of her. I'm the youngest, but I'm also the only daughter. Both of my brothers made the decision to bow out. (Grrrr....)
It was so hard, I was taking care of another person, working full time and also caring for my own family.
My therapist recommended a book called "The 36-Hour Day". The book addressed so many of the things I was going through that I had almost every paragraph highlighted. I'm the baby of the family and have always been treated as such - so , sibling roles had to shift. This was difficult on everyone.
This is just an example of some of the steps we have to take and changes we have to make to not only take care of our loved ones, but also to care for ourselves.
I'd recommend reading the book (both you and your wife) - it certainly helped us gain some perspective on our situation and where our mom might be coming from and where she may be headed. I hope this helps. And best of luck to you, it's not easy.